Chemistry Department of Apparel Manufacturing & Technology BGMEA University of Fashion & Technology

1. BGMEA University of Fashion & Technology
Department of Apparel Manufacturing & Technology
Course Code: CHEM-1101
Course Title: Chemistry
Assignment
Assignment Name: Empirical formula and typical
question related mathematical problem.
Submitted To: Submitted By:
Dr. Md. Mohibul Islam Khan Prosanto Saha
Assistant Professor ID: 201-120-101
BUFT Batch:201, AMT-3

2. 1. Benzoic acid is a white, crystalline powder used as a food
preservative. The compound contains 68.8% C, 5.0% H, and
26.2% O, by mass. What is its empirical formula?
Lat’s consider the total weeight of the gass composition is 100
The molar amount of, C=
.
= 5.7333
The molar amount of, H=
.
= 5.0
The molar amount of, O=
.
= 1.63
The molar ratio of, C=
.
.
= 3.501≅ 3.5
The molar ratio of, H=
.
= 3.053~3
The molar ratio of, O=
.
.
= 1
Thus, the empirical formula benzoic acid is C3.5H3O
= (C3.5H3O)2
=C7H6O2

3. 2. We found the percentage composition of acetic acid to be 39.9%
C, 6.7% H, and 53.4% O. Determine the empirical formula. The
molecular mass of acetic acid was determined by experiment to
be 60.0 amu. What is its molecular formula?
Given that,
Lat’s consider the total weeight of the gass composition is 100
The molar amount of, C=
.
= 3.32
The molar amount of, H=
.
= 6.7
The molar amount of, O=
.
= 3.33
The molar ratio of, C=
.
.
= 1
The molar ratio of, H=
.
.
= 2.02 ≅ 2
The molar ratio of, O=
.
.
= 1
The empirical formula of the composition is= 𝐶𝐻2O
The molecular mass of acetic acid is 60.0 amu
Since, the empirical formula is CH2O the molecular formula will be
(CH2O)n= CnH2nOn
The mass of empirical formula of the compound
stands=(12+1×2+16)=30 and molecular mass 60.

4. Therefore, n=
n= = 2
Thus, the molecular formula the compound is C2H4O2
3. The percentage composition of acetaldehyde is 54.5% C, 9.2% H,
and 36.3% O, and its molecular mass is 44 amu. Obtain the
molecular formula of acetaldehyde.
Lat’s consider the total weeight of the gass composition is 100
The molar amount of, C=
.
= 4.54
The molar amount of, H=
.
= 9.2
The molar amount of, O=
.
= 2.26
The molar ratio of, C=
.
.
= 2
The molar ratio of, H=
.
.
= 4
The molar ratio of, O=
.
.
= 1
The empirical formula of the composition is=C2H4O
The molecular mass of acetic acid is 44 amu

5. Since, the empirical formula is C2H4O the molecular formula will be
(C2H4O)n
The mass of empirical formula of the compound
stands=(12×2+1× 4 +16)=44 and molecular mass 44.
Therefore, n=
n= = 1
Thus, the molecular formula the compound is C2H4O
4. Oxalic acid is a toxic substance used by laundries to remove rust
stains. Its composition is 26.7% C, 2.2% H, and 71.1% O (by
mass), and its molecular mass is 90 amu. What is its molecular
formula?
Lat’s consider the total weeight of the gass composition is 100
The molar amount of, C=
.
= 2.225
The molar amount of, H=
.
= 2.2
The molar amount of, O=
.
= 4.44

6. The molar ratio of, C=
.
.
= 1
The molar ratio of, H=
.
.
= 1
The molar ratio of, O=
.
.
= 2
The empirical formula of the composition is= 𝐶𝐻O2
The molecular mass of the compound is 90 amu
Since, the empirical formula is CHO2 the molecular formula will be
(CHO2)n= CnH2nOn
The mass of empirical formula of the compound
stands=(12+1+16× 2)=45 and molecular mass 90.
Therefore, n=
n= = 2
Thus, the molecular formula the compound is C2H2O4

7. 5. Give examples of an element,a compound,a heterogeneous
mixture, and a homogeneous mixture.
Element: Element are the pure substances containing only one kind
of atoms.
Example: Iron is made of iron atoms so iron can be defined as
elements.
Compound: Any substance composed of identical molecules
consisting of atoms of two or more chemical elements can be called
compound.
Example: Water is a compound because it is made up of more than
one element-hydrogen and oxygen.
Example of Heterogeneous Mixture:
i. Concrete is heterogeneous mixture of an aggregate cement &
water.
ii. Ice cubes in cola from a heterogeneous mixture.
Example of Homogeneous Mixture:
Homogeneous mixture can be defined as solid mixture,liquid
mixture,gaseous mixture.
Such like: sugar water,sodas,bronze,blood plasma,dishwashwashing
detergents.

8. 6. What distinguishes an element from a compound? Can a
compound also be an element?
Elements are pure substances and they are composed of only one
type of atom and compounds are formed by two or more different
types of elements that are united chemically in fixed proprotions and
it is the main way to distinguish elements from compound.
A pure element cannot be a compound.
7. What is meant by the precision of a measurement? How is it
indicated?
The precision of a measurement system is refers to how close the
agreement is between to how close the agreements is between
repeated measurements which are repeated measurements which
are repeated under the same conditions.
One way to analyze the precision of the measurement would be to
determine the range or difference between the lowest and highest
measured values. In that case, the lowest value is 10.9 in and the
highest value is 11.2 in.

9. 8. Two rules are used to decide how to round the result of a
calculation to the correct number of significant figures. Use a
calculation to illustrate each rule.Explain how you obtained the
number of significant figures in the answers?
•Procedure to determine significant figures after multiplication or
division:
1. Multiply or divide the numbers using our calculator.
2. Round the result to have the same number of significant figures
as the measured value with the least number of significant figures.
• Below are two examples.
A) Write the product of 2.10 × 0.5896 with the correct number of
significant figures.
Step 1) 2.10 × 0.5896 = 1.23816
Step 2) 1.23816 = 1.24 (three sig. figs because 2.10 has three)
The answer is 1.24
B) Write the quotient of 16.15/2.7 with the correct number of
significant figures.
Step 1) 16.15 / 2.7 = 5.98148148
Step 2) 5.98148148 = 6.0 (two sig. figs because 2.7 has two)
The answer is 6.0

10. 9. Consider three masses that you wish to add together: 3 g,1.4 g,
and 3.3 g.These numbers represent measured values.Add the
numbers together and report your answer to the correct number
of significant figures?
The three given masses are 3.0g,1.4g, and 3.3g
Add the together and we get= (3.0+1.4+3.3)g
=7.7g
After adding the mass values the result value 7.7
Contain two significant numbers.
10. How many significant figures are there in each of the
following measurements?
a. 73.0000 g b. 0.0503 kg c. 6.300 cm d. 0.80090 m e. 2.010 s
a) 7.30000- significant figures -6
b) 0.0503- significant figures -3
c) 6.300- significant figures -4
d) 0.80090- significant figures -5
e) 2.010- significant figures -4