unit 6 test moles
record your answer in the blank provided. only the answer in the blank will be graded.

1. what si unit is used to measure the number of representative particles in a substance?
a. kilogram c. kelvin
b. mole d. ampere
2. which answer choice is correctly set up to calculate the molar mass of ca(no₂)₂?
a) 40.078 × 14.007 × 4 × 15.999
b) 40.078 + (2)14.007 + (6)15.999
c) 40.078 + (2)14.007 + (4)15.999
d) (2)40.078 + (2)14.007 + (6)15.999
3. which answer choice is correctly set up to calculate the percent composition of hydrogen in c₁₄h₁₀o₃?
a. $\frac{(10)1.008}{(14)12.011 + (10)1.008 + (3)15.999} × 100$ c. $\frac{1.008}{(14)12.011 + (10)1.008 + (3)15.999} × 100$
b. $\frac{(14)12.011 + (10)1.008 + (3)15.999}{(10)1.008} × 100$ d. $\frac{1.008}{12.011 + 1.008 + 15.999} × 100$
4. succinic acid has an empirical formula of c₂h₃o₂. which of these could be the molecular formula of succinic acid?
a) c₈h₁₀o₈ b) c₂h₄o₂ c) c₆h₉o₆ d) c₃h₆o₃
5. the molecular formula, c₁₂h₂₄o₆ would have which of the following as its empirical formula?
a) c₂h₄o b) c₄h₈o₂ c) cho d) ch₂o
6. what is the molar mass of k₂s?
a. 629.354 g c. 71.164 g
b. 110.262 g d. 303.326 g
7. what is the percent composition of oxygen in aspirin, c₉h₈o₄?
a. 35.52% c. 8.96%
b. 60.00% d. 4.48%
8. what is the molar mass of (nh₄)₂so₄?
a. 118.13 g c. 196.086 g
b. 132.14 g d. 143.025 g

Question

unit 6 test moles
record your answer in the blank provided. only the answer in the blank will be graded.

1. what si unit is used to measure the number of representative particles in a substance?
   a. kilogram  c. kelvin
   b. mole  d. ampere
2. which answer choice is correctly set up to calculate the molar mass of ca(no₂)₂?
   a) 40.078 × 14.007 × 4 × 15.999
   b) 40.078 + (2)14.007 + (6)15.999
   c) 40.078 + (2)14.007 + (4)15.999
   d) (2)40.078 + (2)14.007 + (6)15.999
3. which answer choice is correctly set up to calculate the percent composition of hydrogen in c₁₄h₁₀o₃?
   a. $\frac{(10)1.008}{(14)12.011 + (10)1.008 + (3)15.999} × 100$  c. $\frac{1.008}{(14)12.011 + (10)1.008 + (3)15.999} × 100$
   b. $\frac{(14)12.011 + (10)1.008 + (3)15.999}{(10)1.008} × 100$  d. $\frac{1.008}{12.011 + 1.008 + 15.999} × 100$
4. succinic acid has an empirical formula of c₂h₃o₂. which of these could be the molecular formula of succinic acid?
   a) c₈h₁₀o₈  b) c₂h₄o₂  c) c₆h₉o₆  d) c₃h₆o₃
5. the molecular formula, c₁₂h₂₄o₆ would have which of the following as its empirical formula?
   a) c₂h₄o  b) c₄h₈o₂  c) cho  d) ch₂o
6. what is the molar mass of k₂s?
   a. 629.354 g  c. 71.164 g
   b. 110.262 g  d. 303.326 g
7. what is the percent composition of oxygen in aspirin, c₉h₈o₄?
   a. 35.52%  c. 8.96%
   b. 60.00%  d. 4.48%
8. what is the molar mass of (nh₄)₂so₄?
   a. 118.13 g  c. 196.086 g
   b. 132.14 g  d. 143.025 g

Accepted Answer

### Question 1
# Brief Explanations:
The mole (mol) is the SI unit for the amount of substance, which measures the number of representative particles (atoms, molecules, ions, etc.). Kilogram (kg) is for mass, kelvin (K) for temperature, and ampere (A) for electric current.
# Answer:
b. mole

### Question 2
# Brief Explanations:
For $Ca(NO_2)_2$, calcium ($Ca$) has an atomic mass of $40.078$ g/mol. There are $2$ $NO_2$ groups. In $NO_2$, nitrogen ($N$) has an atomic mass of $14.007$ g/mol and oxygen ($O$) has an atomic mass of $15.999$ g/mol. For $NO_2$, the mass contribution from $N$ is $(1)14.007$ and from $O$ is $(2)15.999$. Since there are $2$ $NO_2$ groups, the total mass contribution from $N$ is $(2)14.007$ and from $O$ is $(4)15.999$. The molar mass formula is $M = 40.078+(2)14.007+(4)15.999$.
# Answer:
c) $40.078+(2)14.007+(4)15.999$

### Question 3
# Brief Explanations:
The formula for percent composition of an element $X$ in a compound $A_xB_yC_z$ is $\text{Percent Composition of }X=\frac{\text{Mass of }X\text{ in compound}}{\text{Molar mass of compound}}\times100$. For $C_{14}H_{10}O_3$, the mass of hydrogen ($H$) is $(10)1.008$ (since there are $10$ $H$ atoms with atomic mass $1.008$ g/mol). The molar mass of $C_{14}H_{10}O_3$ is $(14)12.011+(10)1.008+(3)15.999$ (using atomic masses of $C = 12.011$ g/mol, $H=1.008$ g/mol, $O = 15.999$ g/mol).
# Answer:
a. $\frac{(10)1.008}{(14)12.011+(10)1.008+(3)15.999}\times100$

### Question 4
# Brief Explanations:
The molecular formula is a multiple ($n$) of the empirical formula. For $C_2H_3O_2$, if $n = 4$, the molecular formula is $C_{(2\times4)}H_{(3\times 4)}O_{(2\times4)}=C_8H_{12}O_8$. If $n= 2$, $C_{(2\times2)}H_{(3\times2)}O_{(2\times2)}=C_4H_6O_4$. If $n = 3$, $C_{(2\times3)}H_{(3\times3)}O_{(2\times3)}=C_6H_9O_6$.
# Answer:
c) $C_6H_9O_6$

### Question 5
# Brief Explanations:
To find the empirical formula from the molecular formula $C_{12}H_{24}O_6$, divide each sub - script by the greatest common divisor. The greatest common divisor of $12$, $24$, and $6$ is $6$. So, $C_{\frac{12}{6}}H_{\frac{24}{6}}O_{\frac{6}{6}}=C_2H_4O$.
# Answer:
a) $C_2H_4O$

### Question 6
# Brief Explanations:
For $K_2S$, potassium ($K$) has an atomic mass of $39.098$ g/mol and sulfur ($S$) has an atomic mass of $32.06$ g/mol. The molar mass $M=(2\times39.098)+32.06 = 78.196+32.06=110.256\approx110.262$ g/mol (using approximate atomic masses for calculation).
# Answer:
b. $110.262$ g

### Question 7
# Brief Explanations:
For $C_9H_8O_4$, the molar mass $M=(9\times12.011)+(8\times1.008)+(4\times15.999)=108.099 + 8.064+63.996=180.159$ g/mol. The mass of oxygen is $4\times15.999 = 63.996$ g/mol. The percent composition of oxygen is $\frac{63.996}{180.159}\times100\approx35.52\%$.
# Answer:
a. $35.52\%$

### Question 8
# Brief Explanations:
For $(NH_4)_2SO_4$, nitrogen ($N$): $2\times14.007 = 28.014$, hydrogen ($H$): $8\times1.008=8.064$, sulfur ($S$): $32.06$, oxygen ($O$): $4\times15.999 = 63.996$. The molar mass $M=28.014 + 8.064+32.06+63.996=132.134\approx132.14$ g/mol.
# Answer:
b. $132.14$ g

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