Stoichiometry

STOICHIOMETRY LET’S ROCK WITH STOICHIOMETRY!!!

Let’s rock it!!! http://www.youtube.com/watch?v=rWCv-ymhpfY

Sounds complicated??? Sounds like too much to handle??? No WORRIES….let’s explore!!!

FUN with STOICHIOMETRY!!! Balancing chemical equations Ratio and Proportion Limiting Reagent All You Know About Stoichiometry

BALANCING CHEMICAL EQUATIONS UNDERSTANDING THE PURPOSE OF COEFFICIENTS AND SUBSCRIPTS

Which one would you pick??? ( yellow / red ) Zn + HCl ---> ZnCl 2 + H 2 Zn + 2HCl ---> ZnCl 2 + H 2 (keep your choice in your mind…you might want to change your choice later )

More fun…fun…fun… http://funbasedlearning.com/chemistry/chemBalancer/default.htm

Arrange the atoms in the box to form the respective products (Drag and drop the atoms) HCI + NaOH NaCI + H 2 O H Na O H H CI Na O H CI

Arrange the atoms to form the respective products H 2 SO 4 + 2NaOH Na 2 SO 4 + 2H 2 O H H S Na O O O O O H H Na O H H H H O O O O O O Na Na S

Arrange the atoms to form the reactants and the products 2Mg + O 2 2 MgO REACTANTS Mg Mg O O PRODUCTS Mg Mg O O

The law of conservation of mass states that matter can neither be created nor destroyed Thus, in a chemical reaction atoms are neither created nor destroyed, only rearranged in a chemical reaction Thus, the number of a particular atom is the same on both sides of a chemical equation

C 2 H 4 + O 2 CO 2 + H 2 O C H O LEFT RIGHT 2 4 2 3 2 1 F I R S T

Add coefficient 2 in front of CO2 – that balances the carbon (C) Then add coefficient 2 in front of H 2 O – that balances the hydrogen (H) Finally re-calculate how many oxygen atoms you have Now you have 6 oxygen atoms all together on your right To balance that add coefficient 3 in front of O 2 – that balances the oxygen S E C O N D

C 2 H 4 + 3O 2 2CO 2 + 2H 2 O C H O LEFT RIGHT 2 4 6 6 4 2 F I N A L L Y

Coefficient and subscript 5 H 2 What number represents the coefficient? 5 What number represents the Subscript? 2 How many “H’s” do you have? 10

How many Aluminium and Chlorine atoms are present in 2 Aluminium chloride molecules? 2AICI 3 Aluminium = Chlorine = 6 2

SUBSCRIPT AND COEFFICIENT Balance the following equation using the coefficient given AI + HCI AICI 3 + H 2 3 2 6 2

2AI + 6HCI 2AICI 3 + 3H 2 AI H CI H CI H CI H CI H CI H CI AI AI CI CI CI AI CI CI CI H H H H H H Are the number of each atom present on the left (reactant) and the right (product) the same?

SHARPEN YOUR SKILLS!!! HOME http://funbasedlearning.com/chemistry/chemBalancer/default.htm

Mary was home alone…. She was craving for pancakes … She remembered that her mum always kept a stock of pancake mixture in the kitchen … She grabbed the box... And started reading the instructions…

This is what the instruction said… 4 cups of mixture 2 cups of water 4 eggs Mix all, Beat well!!! Note : Each pack makes 12 large pancakes

But 12 is too many!!! She wanted only 3… Hmm…can you help her with the pancake mixture?

4 cups of mixture 2 cups of water 4 eggs 12 pancakes ?eggs 3 pancakes ? cups of mixture ? cups of water Can you help her with the correct measurements to make just 3 pancakes???

Consider the equation once again…. Look at the proportion of the mixture to the number of pancakes… 4 cups of mixture makes 12 pancakes… 4 cups of mixture 12 pancakes 3 pancakes ? cups of mixture 12/4 ? Can you decide how many cups of mixture will be needed?

That was pretty simple!!! Now, can you get the proportion of the rest of the ingredients for Mary? (work it out on a piece of paper and check to see later if you have got the proportions correct)

4 cups of mixture 2 cups of water 4 eggs 12 pancakes ?eggs 3 pancakes ? cups of mixture ? cups of water 1 egg 3 pancakes 1 cup of mixture ½ cup of water ÷4 ÷4 ÷4 ÷4

The pancakes turned out so well for a first timer…Mary loved it !!! THANK YOU!

Can you apply the same idea here??? 1 mole of hydrochloric acid react with 1 mole of Sodium hydroxide solution to form 1 mole of sodium chloride and 1 mole of water. Can you figure out how many moles of water will be produced if 0.5 mole of acid is used???

How many moles of water produced??? HCl + NaOH NaCl + H 2 O 1 1 1 1 Can you determine how many mole of water will be produced if 0.5 mole of acid is used???

Now… consider this equation! H 2 SO 4 + 2NaOH Na 2 SO 4 + 2H 2 O How many moles of sodium sulphate by proportion will be produced if 1 mole of sodium hydroxide is used? 1.0 0.5 2.0 0.25

Now let’s get into the lab and do some ‘real’ stuffs!!! (download the virtual lab above!!!then we can get into action….) http://www.chemcollective.org/vlab/vlab.php

One final task before getting started!!! Explore the reagents and the apparatus provided in the virtual lab… Explore your virtual lab!!! Get familiarized with it…

Get your task sheet and get going with your virtual lab… You are suppose to complete the task given using your virtual lab tools Get the word document ‘ FUN WITH VIRTUAL LAB’ http://www.scribd.com/doc/66347972

Now more exciting activities… Beginner Intermediate Advance

John was making tables for a school project…he needs help… 1m 2 of plank makes 2 table tops. He was thinking how many table tops can be made out of 2m 2 of plank? tell him… 6 8 3 4

Mak Lijah uses 30 eggs and 5kg of flour to make 100 bahulu cakes. How many eggs and how much flour will she need if a customer ordered only 50 bahulu cakes? 20 eggs and 3kg of flour 15 eggs and 2.5kg of flour 15 eggs and 3kg of flour 10 eggs and 2.5kg of flour

1 mol of hydrochloric acid react with 1 mol of sodium hydroxide solution to produce 1 mol of sodium chloride salt and 1mol of water. How many moles of water will be produced if 0.8 mol of acid was used? HCI + NaOH NaCI + H 2 O 0.8 mol 1.0 mol 0.6 mol 0.5 mol

Based on the above chemical equation, can you deduce how many moles of water will be produced if 0.5 mole of sulphuric acid is used? H 2 SO 4 + 2NaOH NA 2 SO 4 + 2H 2 O 0.5 mol 1.5 mol 1.0 mol 0.3 mol

Sulphuric acid react with magnesium to produce magnesium sulphate and hydrogen gas. Pick the correct equation representing the chemical reaction above. H 2 SO 4 + Mg 2MgSO 4 + H 2 H 2 SO 4 + Mg MgSO 4 + H 2 H 2 SO 4 + 2Mg Mg 2 SO 4 + H 2 2H 2 SO 4 + Mg 2MgSO 4 + H 2

H 2 SO 4 + Mg MgSO 4 + H 2 Tip : You may need paper, pen and a calculator If 24g of magnesium is used in the above reaction, how many moles of hydrogen gas will be produced?[Relative atomic mass of magnesium: 24] 2 moles 0.5 mole 1 mole 3 moles

How many moles of hydrogen gas will be produced if Hydrochloric acid is used instead of sulphuric acid? (the mass of the magnesium used is still the same) 2HCI + Mg MgCI 2 + H 2 2 moles 0.5 mole 1 mole 3 moles

2AI + 6HCI 2AICI 3 + 3H 2 30cm 3 of hydrochloric acid with the concentration of 0.2 moldm -3 was used in this experiment. What is the volume of hydrogen gas that will be produced? [Molar volume of gas: 24 dm 3 mol -1 ] 60cm 3 0.06cm 3 72dm 3 72cm 3

C 2 H 4 + 3O 2 2CO 2 + 2H 2 O What is the minimum volume of oxygen gas is required for you to produce 0.6 moles of carbon dioxide gas? [molar volume of gas: 24 dm 3 mol -1 ] 0.9 dm 3 22 dm 3 21.6 dm 3 0.3 dm 3

Al + 3Cu(NO 3 ) 2 2Al(NO 3 ) 3 +3Cu How many grams of copper will be produced if 0.3 moles of Aluminium is used? (Copper (II)nitrate solution is used in excess & RAM of Copper :64 ) 20.1g 28.8g 16.9g 10.3g

More + Less = LESS http://www.youtube.com/watch?v=RO1kErdVqqw

Can you answer these questions??? Why only 30.5cm 3 of hydrogen gas liberated although the same amount of acid was used in both experiments? Why does the amount of hydrogen gas liberated remain at 61cm 3 although zinc was used in excess? (think about it…and jot down what ever you think the reason is on a piece of paper…)

OBJECTIVE At the end of the lesson: Determine which of two reactants is a limiting reagent Calculate the amount in moles or grams of a product, given the amounts in moles or masses in grams of two reactants, one which is in excess .

LET’S BUILD STOOLS 1 TOP and 3 LEGS 1 STOOL

LET’S BUILD STOOLS 1 TOP and 6 LEGS ?

Yes…you are right!!! It is always the top which determines the maximum number of stools that can be built… therefore the top is the limiting factor…

What is a limiting reactant? A limiting reactant is the reactant that limits the amount of another reactant that can combine and the amount of product that can be formed in a chemical reaction The excess reactant is the substance that is not used up completely in a reaction

5 oxygen molecules 5 carbon atoms 10 oxygen molecules 5 carbon dioxide molecules

Which one is the limiting reagent in the reaction between carbon and oxygen? Which reagent was used in excess? What need to be added to increase the amount of carbon dioxide produced? Carbon atoms Oxygen molecules Carbon atoms

Let’s do this together… What is the maximum mass of sodium chloride that can be formed when 50cm 3 of hydrochloric acid with the molarity of 1.0 mol dm -3 reacts with 25cm 3 of sodium hydroxide solution with the same molarity?

HCI + NaOH NaCI +H 2 O V= 50cm 3 M=1.0mol/ dm 3 V= 25cm 3 M=1.0mol/ dm 3 Mass=? How would you determine what is the maximum mass of sodium chloride that can be produced ?

Inspect the equation to check if it was balance Calculate the number of mole of the reactants given to you Determine the limiting reagent Calculate the maximum mass of sodium chloride that can be obtained

To complete a car, four tires will be needed for each cars. How many cars can be completed if there are 100 cars and only 320 tires available? 85 95 90 80

Mg + H 2 SO 4 MgSO 4 + H 2 0.5 mol 1.0 mol If 0.5 mol magnesium and 1.0mol of sulphuric acid is reacts together in a n experiment, only 0.5mol of hydrogen gas was produced. Which one is the limiting reagent in the above reaction? magnesium Sulphuric acid hydrogen Magnesium sulphate

What needs to be added to maximize the production of hydrogen gas in the previous reaction? Volume of hydrogen No of mole of hydrogen No of mole of magnesium No of mole of sulphuric acid

When copper (II) chloride reacts with sodium nitrate, copper (II) nitrate and sodium chloride are formed. Select a balanced equation for the above reaction 2CuCI 2 + NaNO 3 2NaCI + CuNO 3 CuCI 2 + 2NaNO 3 2NaCI + Cu(NO 3 ) 2 2CuCI 2 + NaNO 3 NaCI + 2CuNO 3 CuCI 2 + 2NaNO 3 NaCI + Cu(NO 3 ) 2

If 15 grams of copper (II) chloride reacts with 20 grams of sodium nitrate, how much sodium chloride can be formed? 11g 13g 10g 12g

What is the limiting reagent for the reaction in the previous question? Copper chloride Copper Sodium nitrate Sodium chloride

If there is 35.0 grams of C 6 H 10 and 45.0 grams of O 2 , how many grams of the excess reagent will remain after the reaction ceases? 6 C 6 H 10 + 17 O 2 ---> 12 CO 2 + 10 H 2 O 0.2g of oxygen 6.4g of oxygen 1.207g of oxygen 0.083g of oxygen

Aluminum reacts with chlorine gas to form Aluminum chloride via the following reaction: Al + 3Cl 2 ---> 2AlCl 3 .How many grams of aluminum chloride could be produced from 34.0g of aluminum and 39.0 g of chlorine gas? 48.9g 50.9g 49.9g 51.9g

Suppose 316.0 g of aluminum sulfide reacts with 493.0 g of water. What mass of the excess reactant remains? The unbalanced equation is: Al 2 S 3 + H 2 O ---> Al(OH) 3 + H 2 S 265.5 g of aluminium sulphide 493 g of aluminium sulphide 265.5 g of water 227.5 g of water

OBJECTIVE Applying all the three important concepts in stoichiometry : (i) Balancing chemical equations (ii) Ratio and proportion (iii) Limiting reagent

STOICHIOMETRY Well…it is not that difficult! there are only five steps to remember…

Interpret the question to form a chemical equation Recognize unbalanced and balanced reaction equations Balance the unbalanced equation Explain excess and limiting reagent Calculate the mass of the yield

We have discovered all these steps separately in our previous lessons…now we will look at some worked examples which combines all these steps to help you solve stoichiometry problems….

Let us look at some solved examples…

25g of sodium chloride reacts with 50cm 3 of silver nitrate solution with the concentration of 1.0 mol dm -3 . What is the maximum amount of silver chloride produced? Which one is the limiting reagent?

Interpret the question to form a chemical equation 25g of sodium chloride reacts with 50cm 3 of silver nitrate solution with the concentration of 1.0 mol dm -3 . What is the maximum amount of silver chloride produced? Which one is the limiting reagent? NaCI + AgNO 3 AgCI + NaNO 3

Recognize unbalanced and balanced reaction equations NaCI + AgNO 3 AgCI + NaNO 3 Na Cl Ag 1 1 1 1 1 1 NO 3 1 1 BALANCED

This reaction is a balanced one… no coefficient needs to be added for balancing purposes… Balance the unbalanced equation

Explain excess and limiting reagent NaCI + AgNO 3 AgCI + NaNO 3 n NaCI = Mass/ RMM = 25/(23 + 35.5) = 0.42 mol n AgNO3 = Mass/ RMM = 50/[108+14+3(16)] = 0.29 mol The limiting reagent in this experiment is Silver nitrate as the number of moles of it used is fewer than the number of moles of sodium chloride used

Mass of yield, AgCI = 0.29 mol X (108 + 35.5) gmol -1 = 41.62g Calculate the mass of the yield n= mass/RMM So, mass = n X RMM

In a metal displacement reaction,65g of aluminium reacted with 100g of Iron (ii) Oxide. What will be the excess reagent at the end of the experiment? What needs to be added to maximize the production of Iron?

Interpret the question to form a chemical equation In a metal displacement reaction,65g of aluminium reacted with 150g of Iron (ii) Oxide. What will be the excess reagent at the end of the experiment? What needs to be added to maximize the production of Iron? Al + Fe 2 O 3 Al 2 O 3 + Fe

Recognize unbalanced and balanced reaction equations Al + Fe 2 O 3 Al 2 O 3 + Fe Al Fe O 1 2 3 3 1 2 UNBALANCED

Balance the unbalanced equation Al + Fe 2 O 3 Al 2 O 3 + Fe Al Fe O 1 2 3 3 1 1 BALANCED! X 2 X 2 2Al + Fe 2 O 3 Al 2 O 3 + 2Fe

Explain excess and limiting reagent 2Al + Fe 2 O 3 Al 2 O 3 + 2Fe n Al = Mass/ RMM = 65/27 = 2.41 mol n =Mass/ RMM = 150/[2(56) + 3(16)] = 0.94mol The Excess reagent in this experiment is Aluminium as the number of moles of it used is more than the number of moles of Iron (II) Oxide used Fe 2 O 3

Calculate the mass of the yield No calculation for the amount of yield for this question, but it requires you to decide which reactant needs to be added to maximize the mass of yield Increase the mass of Iron(II) Oxide as it is the limiting reagent in this experiment!

50cm 3 of Sodium Hydroxide with the concentration of 0.2mol/dm 3 was used to neutralize 35cm 3 of sulphuric acid with the same concentration. What will be the maximum mass of water produced? Which one is the limiting reagent in the above reaction?

Interpret the question to form a chemical equation 50cm 3 of Sodium Hydroxide with the concentration of 0.2mol/dm 3 was used to neutralize 35cm 3 of sulphuric acid with the same concentration. What will be the maximum mass of water produced? Which one is the limiting reagent in the above reaction? NaOH + H 2 SO 4 Na 2 SO 4 +H 2 O

Recognize unbalanced and balanced reaction equation NaOH + H 2 SO 4 Na 2 SO 4 +H 2 O Na O H 1 5 3 2 5 2 S 1 1 UNBALANCED

Balance the unbalanced equation NaOH + H 2 SO 4 Na 2 SO 4 +H 2 O 2NaOH + H 2 SO 4 Na 2 SO 4 + 2H 2 O Balancing the number of Sodium atoms, oxygen and hydrogen atoms will balance out the other elements…You don’t really have to balance each and everyone of them… BALANCED!

Explain excess and limiting reagent 2NaOH + H 2 SO 4 Na 2 SO 4 + 2H 2 O n NaOH = MV/1000 = (50 X 0.2)/1000 = 0.01 mol n =MV/ 1000 = (35 X 0.2)/1000 = 0.007mol The limiting reagent in this experiment is sulphuric acid as the number of moles of it used is fewer than the number of mol of sodium hydroxide solution used H 2 SO 4 H 2 SO 4

From the equation, two moles of water is produced by proportion. Meaning the number of moles of water produced is = 0.007 X 2 = 0.014mol Mass of yield, H 2 O = 0.014 mol X [2(1) + 16] gmol -1 = 0.252 g Calculate the mass of the yield n= mass/RMM So, mass = n X RMM

More and more fun activities… Please try to solve them before looking at the solutions!!! http://misterguch.brinkster.net/PRA004.pdf http://misterguch.brinkster.net/PRA048.pdf http://misterguch.brinkster.net/PRA019.pdf

This equation is balanced… Now you can proceed to the next step! HCI + NaOH NaCI +H 2 O BACK

n = MV n HCI = MV = [(1.0 mol/dm 3 ) (50 cm 3 )]÷1000 = 0.05 mol n NaOH = MV = [(1.0 mol/dm 3 ) (25 cm 3 )]÷1000 = 0.025 mol BACK

n HCI = 0.05 mol n NaOH = 0.025 mol NaOH will be the limiting reagent as it is the limited one here. Only 0.025 mol of it is present. BACK

From the equation, 1 mol of sodium hydroxide solution produces 1 mole of sodium chloride salt Therefore, 0.025mol of sodium hydroxide solution would produce 0.025 mol of sodium chloride salt

n HCI = n NaCI = 0.025 mol Mass = No. of mol x Relative molecular mass = 0.025mol x (23 + 35.5) = 0.025mol x 58.5 g/mol = 1.46g BACK

Stoichiometry

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Stoichiometry