Question

question 7
6 pts
how many moles are present in 140. g of cacl₂?
1.46 mol
0.793 mol
1.26 mol
15500 mol
question 8
6 pts
how many total atoms are present in 0.140 g of hcl?
1.20×10²⁴ atoms
4.57×10²² atoms
4.62×10²¹ atoms
2.31×10²¹ atoms

Explanation:

Step1: Calculate molar mass of $CaCl_2$

The molar mass of $Ca$ is approximately $40.08\ g/mol$, and the molar mass of $Cl$ is approximately $35.45\ g/mol$. For $CaCl_2$, the molar mass $M = 40.08+2\times35.45=40.08 + 70.9=110.98\ g/mol$.

Step2: Calculate moles of $CaCl_2$

Use the formula $n=\frac{m}{M}$, where $m = 140\ g$ and $M = 110.98\ g/mol$. So $n=\frac{140}{110.98}\approx1.26\ mol$.

Step3: Calculate molar mass of $HCl$

The molar mass of $H$ is approximately $1.01\ g/mol$ and of $Cl$ is approximately $35.45\ g/mol$. So the molar mass of $HCl$, $M_{HCl}=1.01 + 35.45=36.46\ g/mol$.

Step4: Calculate moles of $HCl$

Using the formula $n=\frac{m}{M}$, with $m = 0.140\ g$ and $M = 36.46\ g/mol$, we get $n=\frac{0.140}{36.46}\ mol$.

Step5: Calculate number of molecules of $HCl$

Use Avogadro's number $N_A = 6.022\times 10^{23}\ molecules/mol$. The number of $HCl$ molecules $N_{molecules}=n\times N_A=\frac{0.140}{36.46}\times6.022\times 10^{23}$.

Step6: Calculate total number of atoms in $HCl$

Since each $HCl$ molecule has 2 atoms, the total number of atoms $N_{atoms}=2\times\frac{0.140}{36.46}\times6.022\times 10^{23}\approx4.62\times 10^{21}$ atoms.

Answer:

Question 7: C. 1.26 mol
Question 8: C. $4.62\times 10^{21}$ atoms