# 4: Stoichiometry. Quantitative Information about Chemical Reactions

## Stoichiometry

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Exercise $$\PageIndex{1}$$

The thermal decompostion of potassium chlorate results in the formation of potassium chloride and oxygen. How many grams of potassium chloride are formed when 2.45 g of potassium chlorate completely decomposed?

a. 0.89g

b. 2.45g

c. 1.49g

d. 0.097g

c. 1.49g

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Exercise $$\PageIndex{1}$$

The thermal decompostion of potassium chlorate results in the formation of potassium chloride and oxygen. How many grams of oxygen are formed when 2.45 g of potassium chlorate is completely decomposed?

a. 0.98g

b. 2.45g

c. 0.87g

d. 0.960g

d. 0.960g

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Exercise $$\PageIndex{1}$$

Magnesium hydroxide reacts with phosphoric acid to produce magnesium phosphate and water. What is the maxiumum quantity (in grams) of magnesium phosphate that can be produced if 2.00 g of magnesium hydroxide is added to 2.10g of phosphoric acid?

a. 2.81g

b. 3.67g

c. 2.0g

d. 2.10g

a. 2.81g

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Exercise $$\PageIndex{1}$$

A student performs the reaction in question 3 and gets a yield of 2.67g. What is the percent yield of the students work?

a. 105%

b. 100%

c. 88.0%

d. 95.0%

d. 95.0%

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Exercise $$\PageIndex{1}$$

How many grams of CaCl2 can be formed from 150.g HCl? Assume excess CaO. The unbalanced reaction is

$$C a O+H C l \rightarrow C a C l_{2}+H_{2} O$$

a. 114g

b. 48.6g

c. 228g

d. NOTA

c. 228g

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Exercise $$\PageIndex{1}$$

How many grams of Fe(NO3)3 can be formed from 75.9g Fe2S3? Assume excess HNO3. The unbalanced reaction is

$$Fe_{2} S_{3}+H N O_{3} \rightarrow H_{2} S+Fe(NO_{3})_{3}$$

a. 331g

b. 44.2g

c. 177g

d. NOTA

c. 177g

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Exercise $$\PageIndex{1}$$

How many grams of Na2S can be formed from 115g NaCl? Assume excess Fe2S3. The unbalanced reaction is

$$Fe_{2} S_{3}+NaCl \rightarrow Na_{2} S+FeCl_{3}$$

a. 76.8g

b. 19.8g

c. 153.6g

d. NOTA

a. 76.8g

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Exercise $$\PageIndex{1}$$

How many grams of Mg3N2 can be formed from 75.0g Mg(OH)2? Assume excess NH3. The unbalanced reaction is

$$Mg(OH)_{2}+NH_{3} \rightarrow MgN_{2} + H_{2}O$$

a. 14.4g

b. 43.3g

c. 129g

d. NOTA

b. 43.3g

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Exercise $$\PageIndex{1}$$

How many grams of Ca3(PO4)2 can be formed from 175g Ca(OH)2? Assume excess H3PO4. The unbalanced reaction is

$$Ca(OH)_{2}+H_{3}PO_{4} \rightarrow Ca_{3}(PO_{4})_{2} + H_{2}O$$

a. 314g

b. 244g

c. 58.3g

d. NOTA

b. 244g

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Exercise $$\PageIndex{1}$$

How many grams of CaO will react with 150.0g HCl? The unbalanced reaction is

$$CaO +HCl \rightarrow CaCl_{2} + H_{2}O$$

a. 194.9g

b. 115.4g

c. 150.0g

d. NOTA

b. 115.4g

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Exercise $$\PageIndex{1}$$

What is the percent yield of CaCl2 if 76.1g of CaCl2 is formed for the reaction in question 1? The unbalanced reaction is

$$CaO +HCl \rightarrow CaCl_{2} + H_{2}O$$

a. 33.3%

b. 76.1%

c. 66.8%

d. NOTA

a. 33.3%

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Exercise $$\PageIndex{1}$$

What is the percent yield of Fe(NO3)3 if 146g of Fe(NO3)3 is formed? The unbalanced reaction is

$$Fe_{2} S_{3}+H N O_{3} \rightarrow H_{2} S+Fe(NO_{3})_{3}$$

a. 82.5%

b. 41.3%

c. 74.2%

d. NOTA

a. 82.5%

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Exercise $$\PageIndex{1}$$

What is the percent yield of Fe(NO3)3 if 146g of Fe(NO3)3 is formed? The unbalanced reaction is

$$Fe_{2} S_{3}+H N O_{3} \rightarrow H_{2} S+Fe(NO_{3})_{3}$$

a. 82.5%

b. 41.3%

c. 74.2%

d. NOTA

a. 82.5%

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Exercise $$\PageIndex{1}$$

How many grams of H3PO4 will react with 175g of Ca(OH)2? The unbalanced reaction is

$$Ca(OH)_{2}+H_{3}PO_{4} \rightarrow Ca_{3}(PO_{4})_{2} + H_{2}O$$

a. 51.3g

b. 154g

c. 347g

d. NOTA

b. 154g

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Exercise $$\PageIndex{1}$$

What is the percent yield of Ca3(PO4)2 if 93g of Ca3(PO4)2 is formed? The unbalanced reaction is

$$Ca(OH)_{2}+H_{3}PO_{4} \rightarrow Ca_{3}(PO_{4})_{2} + H_{2}O$$

a. 98.6%

b. 76.2%

c. 38.1%

d. NOTA

c. 38.1%

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Exercise $$\PageIndex{1}$$

How many grams of O2 is present upon completion of a reaction with 67.0 grams of C and 194 grams of O2. The unbalanced reaction is

$$C+O \rightarrow C O_{2}$$

a. 0.00g

b. 16.0g

c. 111g

d. NOTA

b. 16.0g

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Exercise $$\PageIndex{1}$$

How many grams of O2 is present upon completion of a reaction with 67.0 grams of C and 194 grams of O2. The unbalanced reaction is

$$C+O \rightarrow C O_{2}$$

a. 0.00g

b. 13.0g

c. 27.0g

d. NOTA

a. 0.00g

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Exercise $$\PageIndex{1}$$

If 212g CO2 is produced from the reaction of 67.0 grams of C and 194 grams of O2, what is the percent yield? The unbalanced reaction is

$$C+O \rightarrow C O_{2}$$

a. 86.2%

b. 43.1%

c. 64.2%

d. NOTA

a. 86.2%

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Exercise $$\PageIndex{1}$$

If the percent yield of a reaction of 67.0 grams of C and 194 grams of O2 was 92.1%, how much CO2 is produced? The unbalanced reaction is

$$C+O \rightarrow C O_{2}$$

a. 212g

b. 246g

c. 227g

d. NOTA

c. 227g

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Exercise $$\PageIndex{1}$$

How many grams of oxygen are present upon completion of the reaction of 120. grams of Al and 120. grams of O2? The unbalanced reaction is

$$Al+O_{2} \rightarrow Al_{2} O_{3}$$

a. 120.g

b. 107g

c. 13.0g

d. NOTA

c. 13.0g

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Exercise $$\PageIndex{1}$$

How much Al2O3 is formed from the reaction of 120. grams of Al and 120 grams of oxygen if the percent yield is 91.6%. The unbalanced reaction is

$$Al+O_{2} \rightarrow Al_{2} O_{3}$$

a. 193g

b. 207g

c. 226g

d. NOTA

b. 207g

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## Stoichiometry of Mg(s) and HCl(aq)

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Exercise $$\PageIndex{1}$$

If 1.0 mol of Mg reacts with 3.0 mol of HCl, how many moles of gas will be produced?

a. 0.5mol

b. 1.0mol

c. 2.0mol

d. 3.0mol

b. 1.0mol

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Exercise $$\PageIndex{1}$$

How many moles of gas will be produced from 2.43g of Mg?

a. 0.05mol

b. 0.08mol

c. 0.1mol

d. 2.0mol

c. 0.1mol

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Exercise $$\PageIndex{1}$$

How many grams of gas will be formed if 0.243g of Mg is dissolved completely in the HCl solution?

a. 0.020g

b. 0.030g

c. 0.050g

d. 0.080g

a. 0.020g

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Exercise $$\PageIndex{1}$$

How many moles of gas will be formed if it takes 20.0ml of 0.1M HCl to dissolve all the Mg?

a. 0.1mol

b. 0.01mol

c. 0.002mol

d. 0.001mol

c. 0.002mol

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Exercise $$\PageIndex{1}$$

What is the volume of the gas at STP if 20.0ml of 0.1M HCl is used to dissolve all the Mg? (note, you need to cover gas laws before you can answer this).

a. 2.24L

b. 0.224L

c. 0.0224L

d. 0.0448L

d. 0.0448L

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## Limiting Reagents

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Exercise $$\PageIndex{1}$$

How many grams of CO2 can be formed from 67 grams of C and 194 grams of O2? The unbalanced equation is

$$C+O_{2} \rightarrow CO_{2}$$

a. 250g

b. 270g

c. 44g

d. NOTA

a. 250g

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Exercise $$\PageIndex{1}$$

How many grams of Fe2S3 can be formed from 780 grams of Na2S and 324 grams of FeCl3? The unbalanced equation is

$$Na_{2}S + FeCl_{3} \rightarrow Fe_{2}S_{3} + NaCl$$

a. 416g

b. 324g

c. 208g

d. NOTA

c. 208g

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Exercise $$\PageIndex{1}$$

How many grams of Mg(OH)2 can be formed from 165 grams of H2O and 165 grams of Mg3N2? The unbalanced equation is

$$Mg_{3}N_{2} + H_{2}O \rightarrow Mg(OH)_{2} + NH_{3}$$

a. 165g

b. 268g

c. 495g

d. NOTA

b. 268g

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Exercise $$\PageIndex{1}$$

How many grams of SO2 can be formed from 45.0 grams of S and 60.0 grams of O2? The unbalanced equation is

$$S+O_{2} \rightarrow SO_{2}$$

a. 89.7g

b. 120.5g

c. 60.0g

d. NOTA

a. 89.7g

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Exercise $$\PageIndex{1}$$

How many grams of Al2O3 can be formed from 120. grams of Al and 120. grams of O2? The unbalanced equation is

$$Al+O_{2} \rightarrow Al_{2} O_{3}$$

a. 255g

b. 226g

c. 240g

d. NOTA

b. 226g

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## Molarity Calculations

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Exercise $$\PageIndex{1}$$

3.0g of a substance is dissolved in water. The volume of this solution is 40.0ml. What is the molarity of the solution? (The molecular weight of the substance is 63.4g/mol.)

a. 1.2M

b. 0.0012M

c. 2.8M

d. None of the above

a. 1.2M

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Exercise $$\PageIndex{1}$$

A student is performing an experiment with 30.0ml of an unknown solution that has a molarity of 5.0M. How many moles are present in the unknown solution?

a. .091mol

b. 1.5mol

c. 0.15mol

d. None of the above

c. 0.15mol

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Exercise $$\PageIndex{1}$$

2.5g of a substance is dissolved in water. The molarity of the solution is 3.0M. What is the volume of the solution? (The molecular weight of the substance is 102.4g/mol.)

a. 73ml

b. 8.1ml

c. 81ml

d. None of the above

b. 8.1ml

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Exercise $$\PageIndex{1}$$

An unknown amount of an unknown is dissolved in water. The molarity of the solution is 3.0M. The volume of the solution 50.0ml. What is the mass of the substance? (The molecular weight of the substance is 21.6g/mol.)

a. 6.9g

b. 0.0069g

c. 3.2g

d. None of the above

c. 3.2g

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## Limiting Reagents and Stoichiometry

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Exercise $$\PageIndex{1}$$

The molarity of Na3PO4 is 8.000x10-2M, and the molarity of BaCl2 is 1.000x10-1M. If you start with 25.00ml of Na3PO4 and 25.00ml of BaCl2, what is the limiting reagent?

a. BaCl2

b. Na3PO4

c. NaCl2

d. None of the above

a. BaCl2

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Exercise $$\PageIndex{1}$$

What is the mass of Ba3(PO4)2(s) after the reaction?(MW=601.93g/mol)

a. 0.5016g

b. 1.384x10-6g

c. 0.1672g

d. None of the above

a. 0.5016g

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Exercise $$\PageIndex{1}$$

What is the concentration of Na+ after the reaction?

a. 0.1000M

b. 0.1200M

c. 0.5000M

d. None of the above

b. 0.1200M

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Exercise $$\PageIndex{1}$$

What is the concentration of Cl- after the reaction?

a. 0.1200M

b. 0.1000M

c. 0.2000M

d. None of the above

b. 0.1000M

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Exercise $$\PageIndex{1}$$

What is the concentration PO4-3 after the reaction?

a. 1.243M

b. 5.000M

c. 6.667x10-3M

d. None of the above