chemist: zion bington
molar mass/percent composition worksheet
instructions: write the formula for the compound given. then find the percent compositions of all of the elements in the following compounds. show all work to receive credit.
1) copper (ii) bromide formula:______
cu:______
br:______
2) sodium hydroxide formula:______
na:______
o:______
h:______
3) ammonium sulfide formula:______
n:______
h:______
s:______
4) dinitrogen disulfide formula:______
n:______
s:______

Question

Accepted Answer

### 1) Copper (II) Bromide
# Explanation:
## Step1: Write the formula
Copper (II) has a charge of $Cu^{2+}$, bromide has a charge of $Br^{-}$. Using the criss - cross method, the formula is $CuBr_{2}$.
## Step2: Calculate molar mass
The atomic mass of $Cu = 63.55\space g/mol$, $Br=79.90\space g/mol$.
Molar mass of $CuBr_{2}=63.55+(2\times79.90)=63.55 + 159.8=223.35\space g/mol$
## Step3: Calculate percent composition of $Cu$
Percent composition of $Cu=\frac{63.55}{223.35}\times100\%\approx28.45\%$
## Step4: Calculate percent composition of $Br$
Percent composition of $Br=\frac{159.8}{223.35}\times100\%\approx71.55\%$

# Answer:
Formula: $CuBr_{2}$
Cu: $28.45\%$
Br: $71.55\%$

### 2) Sodium Hydroxide
# Explanation:
## Step1: Write the formula
Sodium has a charge of $Na^{+}$, hydroxide has a charge of $OH^{-}$. The formula is $NaOH$
## Step2: Calculate molar mass
The atomic mass of $Na = 22.99\space g/mol$, $O = 16.00\space g/mol$, $H=1.01\space g/mol$
Molar mass of $NaOH=22.99 + 16.00+1.01=40.00\space g/mol$
## Step3: Calculate percent composition of $Na$
Percent composition of $Na=\frac{22.99}{40.00}\times100\% = 57.48\%$
## Step4: Calculate percent composition of $O$
Percent composition of $O=\frac{16.00}{40.00}\times100\%=40.00\%$
## Step5: Calculate percent composition of $H$
Percent composition of $H=\frac{1.01}{40.00}\times100\%\approx2.52\%$

# Answer:
Formula: $NaOH$
Na: $57.48\%$
O: $40.00\%$
H: $2.52\%$

### 3) Ammonium Sulfide
# Explanation:
## Step1: Write the formula
Ammonium has a charge of $NH_{4}^{+}$, sulfide has a charge of $S^{2 -}$. Using the criss - cross method, the formula is $(NH_{4})_{2}S$
## Step2: Calculate molar mass
The atomic mass of $N = 14.01\space g/mol$, $H = 1.01\space g/mol$, $S=32.07\space g/mol$
Molar mass of $(NH_{4})_{2}S=(2\times14.01)+(8\times1.01)+32.07=28.02+8.08 + 32.07=68.17\space g/mol$
## Step3: Calculate percent composition of $N$
Percent composition of $N=\frac{28.02}{68.17}\times100\%\approx41.10\%$
## Step4: Calculate percent composition of $H$
Percent composition of $H=\frac{8.08}{68.17}\times100\%\approx11.85\%$
## Step5: Calculate percent composition of $S$
Percent composition of $S=\frac{32.07}{68.17}\times100\%\approx47.05\%$

# Answer:
Formula: $(NH_{4})_{2}S$
N: $41.10\%$
H: $11.85\%$
S: $47.05\%$

### 4) Dinitrogen Disulfide
# Explanation:
## Step1: Write the formula
“Di -” means 2. So the formula is $N_{2}S_{2}$
## Step2: Calculate molar mass
The atomic mass of $N = 14.01\space g/mol$, $S = 32.07\space g/mol$
Molar mass of $N_{2}S_{2}=(2\times14.01)+(2\times32.07)=28.02+64.14 = 92.16\space g/mol$
## Step3: Calculate percent composition of $N$
Percent composition of $N=\frac{28.02}{92.16}\times100\%\approx30.40\%$
## Step4: Calculate percent composition of $S$
Percent composition of $S=\frac{64.14}{92.16}\times100\%\approx69.60\%$

# Answer:
Formula: $N_{2}S_{2}$
N: $30.40\%$
S: $69.60\%$

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QUESTION IMAGE

Question

Explanation:

1) Copper (II) Bromide

Step1: Write the formula

Step2: Calculate molar mass

Step3: Calculate percent composition of \(Cu\)

Step4: Calculate percent composition of \(Br\)

Step1: Write the formula

Step2: Calculate molar mass

Step3: Calculate percent composition of \(Na\)

Step4: Calculate percent composition of \(O\)

Step5: Calculate percent composition of \(H\)

Step1: Write the formula

Step2: Calculate molar mass

Step3: Calculate percent composition of \(N\)

Step4: Calculate percent composition of \(H\)

Step5: Calculate percent composition of \(S\)

Answer:

2) Sodium Hydroxide