Question

Silicon has three naturally occurring isotopes with thefollowing masses and natural abundances:

Isotope Mass ({\rm amu}) Abundance (%)
{\rm Si}-28 27.9769 92.2
{\rm Si}-29 28.9765 4.67
{\rm Si}-30 29.9737 3.10
Calculate the atomic mass of silicon.
b- When solutions of silver nitrate and calcium chloride aremixed, silver chloride precipitates out of solution according tothe equation
2\; \rm AgNO_3 \it (aq) \rm \;+\;CaCl_2 \it (aq) \rm \; \rightarrow \; 2\;AgCl \it (s) \rm\; + \; Ca(NO_3)_2 \it (aq)
What mass of silver chloride can be producedfrom 1.18 L of a 0.113 \it M solution of silver nitrate?
The reaction described required3.28 L of calcium chloride. What is the concentration of thiscalcium chloride solution?
c- A volume of 50.0 mL of aqueous potassium hydroxide (\rm KOH) was titrated against a standard solution of sulfuricacid (\rm H_2SO_4). What was the molarity of the \rm KOH solution if 23.7 mL of 1.50 M\rm H_2SO_4 was needed? The equation is
\rm 2KOH(\it aq\rm )+H_2SO_4(\it aq\rm )\rightarrow\rm K_2SO_4(\it aq\rm )+2H_2O(\it l\rm )
Then, Redox titrations are used to determine the amounts ofoxidizing and reducing agents in solution. For example, a solutionof hydrogen peroxide, \rm H_2O_2, can be titrated against a solution of potassiumpermanganate, \rm KMnO_4. The following equation represents the reaction:
\matrix{{\rm 2KMnO}_4(aq)+{\rm H_2O}_2(aq)+3{\rm H_2SO}_4(aq)\rightarrow&&\hfill\cr\hfill \qquad\qquad\qquad{\rm O}_2(g)+2{\rm MnSO}_4(aq)+{\rm K_2SO}_4 (aq)+4{\rm H_2O}(l)&&\hfill}
A certain amount of hydrogen peroxide was dissolved in 100.\rm mL of water and then titrated with 1.68 M\rm KMnO_4. How much \rm H_2O_2 was dissolved if the titration required13.8 mL of the \rm KMnO_4 solution?

Answer 1

See explanation

Step-by-step explanation:

Relative atomic mass of silicon;

(27.9769 × 0.9218) + (28.9765 × 0.0471) + (29.9738 × 0.0312) = 28.0891

2)

2AgNO3 (aq) + CaCl2(aq) ----> 2AgCl(s) + Ca(NO3)2(aq)

number of moles of silver nitrate = 1.18 L * 0.113 M = 0.133 moles

Since 2 moles of silver nitrate yields 2 moles of silver chloride

0.133 moles of silver nitrate yields 0.133 * 2/2 = 0.133 moles of AgCl

Since 2 moles of silver nitrate reacts with 1 mole of calcium chloride

0.133 moles of silver nitrate reacts with 0.133 moles * 1/2 = 0.0665 moles of CaCl2

n =CV

C =n/V = 0.0665 moles/3.28 L = 0.02 M

3) H2SO4(aq) + 2KOH(aq) -------> K2SO4(aq) + 2H20(l)

CA = concentration of acid = 1.5 M

VA = volume of acid 23.7 ml

CB = concentration of base = ?

VB= volume of base = 50 ml

NA = number of moles of acid =1

Number of moles of base = 2

From;

CAVA/CBVB =NA/NB

CAVANB = CBVBNA

CB = CAVANB/VBNA

CB = 1.5 * 23.7 * 2/ 50 * 2

CB = 0.711 M

4) Number of moles of KMnO4 = 1.68 * 19.8/1000 = 0.033 moles

If 2 moles of KMnO4 reacts with 1 mole of H2O2

0.033 moles of KMnO4 reacts with 0.033 * 1/2 = 0.0165 moles of H2O2

molar mass of H2O2 = 34 g/mol

mass of H2O2 = 0.0165 moles of H2O2 * 34 g/mol = 0.56 g of H2O2