Ex. 2AgNO3(aq) + Na2CrO4(aq) Ag2CrO4 (s) + 2NaNO3(aq)

Page 264 1,2

In writing net ionic equations from double and single replacement reactions, it is necessary to know what “comes apart,” and what doesn’t. The rules are simple. Ionic substances which are soluble according to the solubility table will dissociate when exposed to water, and are written in ionic form. The resultant ions are in (aq) state. Molecules are never “taken apart” into ions, as they are not made up of ions. Acids are all soluble, but only the acids classified as “strong” actually ionize 100%. The other acids do not, and therefore are left in molecular form, or “together.”

Write net ionic equations for the following reactions:

1. Solutions of sodium sulfide and iron(II) sulfate are mixed.

2. A solution of silver nitrate is poured onto a piece of copper.

3. A solution of nitric acid has solid insoluble magnesium oxide added to it.

4. Solutions of hydrocyanic acid and sodium hydroxide are mixed.

5. Carbon dioxide gas is bubbled into lithium hydroxide solution to form water and lithium carbonate.

6. Solutions of sodium carbonate and hydrochloric acid are mixed.

7. Solutions of ammonium phosphate and zinc sulfate mix.

8. Cadmium metal is added to a solution of cobalt(III) nitrate.

9. Ethanoic acid mixes with barium hydroxide solution.

10. When potassium sulfide solution mixes with hydrochloric acid solution, two products form. One of them is H2S(g).

CHAPTER 7Qualitative Analysis Questions

BLM 7.1.5ASSESSMENT

1. The transition metal with a blue colour in solution and a blue flame color is _______________.

2. How could you tell the difference between the following solutions by looking at them?

(a) FeCl3(aq) and FeCl2(aq)

(b) Cr(NO3)3(aq) and Cr(NO3)2(aq)

(c) K2Cr2O7(aq) and K2CrO4(aq)

(d) MnCl2(aq) and KMnO4(aq)

3. What solution could you choose in each case to distinguish between each of the pairs of solutions given by using precipitation?

(a) Sr(NO3)2(aq) and Ca(NO3)2(aq)

(b) NaNO3(aq) and Ca(NO3)2(aq)

(c) AgClO3(aq) and NaClO3(aq)

4. How many colours could you make fireworks if you had access to only alkali metals? If a firework is red, which alkali metal(s) could be responsible?

Page 270 review

7.2 Stoichiometry

Stoichiometry allows us to predict the amount of product that would be formed, or the amount of reactant that is required in order to produce a desired amount of product. It is very useful. It also tells us that if we don’t get the amount calculated that our procedure is not very accurate, or the reaction is not one that uses up ALL of the reactants. It can tell us about the reaction and whether it is a ‘productive’ one.

4 steps of Stoich:

1) Set up balanced equation2) Find moles; n=m/M3) Multiply by the molar ratio; wanted/given4) Answer the question

Gravimetric Stoich: (n=m/M)

Gravimetric stoich involves ‘gravity’! It measures or compares amounts usually based on MASS!

The most common type involves an initial mass of reactant and asks you to solve for the mass of product that would be formed.

However, there are shorter questions in gravimetric stoich that involve a mole amount being given or being found. They are easier to solve because there are less steps, but they are not as practical to use in a lab situation since moles is not a measurable quantity.

We will start with the simpler questions:

Mole to mole:

Has only steps 1 and 3. Step 2 can be skipped because we already know the number of moles. Step 4 can be skipped because we will already have our answer in the quantity we want – MOLES.

Mole to Mass Stoich:

Has steps 1,3, and 4. Step 2 can be skipped since the number of moles of a substance is already known!

Eg. What mass of zinc sulfide could react with 21.0 mol of oxygen to produce zinc oxide and sulfur dioxide?

Mass to Mole Stoich:

Has steps 1,2,and 3. Step 4 can be skipped since the answer was asked for in moles and that will be what you get from step 3.

Eg. Determine the number of moles of sulfuric acid required to react with 62.0 g of calcium phosphate.

Mass to Mass Stoich:

Involves all 4 steps and as previously mentioned, is the most common of the questions in gravimetric stoich.

Eg.

Sheet 7.2.3

Pag 274,278

Solution Stoichiometry: (done in solution unit)

Involves the same steps as any other stoich question, but the formula may be different. Since we don’t measure MASS of a solution, but concentration and volume, then the formula used in step 2 or 4 is the (n=CV). Other than this, everything remains the same.

Eg.

Page 282

Sheet 7.2.5

Investigation 7B pg 282 (sheet 7.2.6)

Gas Stoich (done in gas unit)

Stoichiometry with gases is definitely a much more difficult process to perform in a lab, but it is done under controlled conditions with the proper equipment that can handle pressure, volume, and temperature changes.

Like all chemical reactions, the ratio of molecules or moles in the equation is the ratio that reacts.

The same 4 steps are taken as in all stoich questions, but there is a different equation often used to find the moles of gas, since like solutions, we don’t usually measure the mass of gas. The equation used can be one of two:

n=v/V if the reaction is done under STP or SATP conditions. This way we know the value of the molar volume. If the conditions are different than that of STP or SATP, we will need to know those conditions and can use the ideal gas law PV=nRT (rearranged for moles when required).

Eg. If 300g of propane burns in a gas barbeque, what volume of oxygen at SATP is required for the reaction?

(843L)

eg. Hydrogen gas is produced when sodium metal is added to water. What mass of sodium is necessary to produce 20.0 L of hydrogen at SATP?

(37.1g)

Eg. In an industrial application known as the Haber process, ammonia to be used as fertilizer results from the reaction of nitrogen and hydrogen. What volume of ammonia at 450kPa pressure and 80 degrees Celsius can be obtained from the complete reaction of 7.5 kg of hydrogen?

(16kL)

Page 286,287

Sheets 7.2.7. and 7.2.8

7.2 review page 289-290,

Below are stoichiometry problems involving solutions, gases, and pure substances:

1. Write the reaction for the formation of lithium phosphide from its elements.

(a) How many moles of lithium phosphide form when 3.2 mol of lithium react?

(b) How many grams of lithium react with 0.500 mol of phosphorus?

(c) How many grams of lithium react with 45.0g of phosphorus?

2. Write the reaction between solutions of mercury(II) nitrate and sodium sulfide.

(a) How many moles of sodium nitrate form from the reaction of 2.85 mol of sodium sulfide?

(b) How many litres of 0.150 mol/L mercury(II) nitrate react with 0.540 L of 0.653 mol/L sodium sulfide?

(c) How many grams of precipitate would you get from the reaction of 1.00 L of 0.550 mol/L sodium sulfide with mercury(II) nitrate?

3. Given the reaction between iron(III) oxide and carbon monoxide below, answer the following questions:

Fe2O3(s) + 3CO(g) → 2FeO(s) + 3CO2(g)

(a) How many grams of iron(III) oxide will react with 27.3 L of carbon monoxide at 25.0 oC and 130.5kPa?

(b) How many grams of iron(II) oxide will form from the reaction of 10.7 g of iron(III) oxide?

(c) What volume of carbon monoxide needs to react under STP conditions for 40.8 L of carbon dioxide to form under the same conditions?

Chapter review and test

Chapter 8:

Do pg 299,303 questions

Sheets 8.1.2 and 8.1.5

Pg 304 8.1 review

Pg 303 #11 as intro

Predicted and Experimental Yield

Predicted or theoretical yield=

Experimental or actual yield=

Factors that reduce experimental yield

1. Competing reactions

2. Slow reaction

3. Collection and transfer (mechanical losses)

4. Reactant purity

5. Reaction does not go to completion

%yield= experimental

predicted (stoich) x 100

Why is percent yield important?

Calculating Percent Yield

Page 308 questions

1. N2(g) + 3H2(g) → 2 NH3(g)

When 7.5 × 101 g of nitrogen gas reacts with sufficient hydrogen gas, the theoretical yield of ammonia is 9.10g. If 1.72 g of ammonia is obtained by experiment, what is the percentage yield of the reaction?

2. 20.0 g of bromic acid, HBrO3, is reacted with excess HBr.

HBrO3(aq) + 5HBr(aq) → 3H2O(ℓ) + 3Br2(aq)

(a) What is the predicted yield of Br2 for this reaction?

(b) If 47.3 g of Br2 is produced, what is the percentage yield of Br2?

3. In order to produce a lead(II) chromate precipitate, lead(II) chloride reacts with sodium chromate in solution. A 12.5 g mass of lead(II) chloride is mixed into solution, and is allowed to react with excess sodium chromate.

(a) What is the predicted yield of lead(II) chromate?

(b) Calculate the percentage yield if 13.8 g of lead(II) chromate is produced experimentally.

CHAPTER 8Percentage Yield Problems (continued)

BLM 8.2.1ASSESSMENT

4. When calcium carbonate reacts with hydrogen chloride, the products are calcium chloride, carbon dioxide and water. If this reaction occurs with 81.5% yield, what mass of carbon dioxide will be collected if 15.7 g of calcium carbonate is added to sufficient hydrogen chloride?

Investigation 8B (sheet 8.2.2)

8.2 review

8.3 ACID –BASE TITRATION

Titrant: is the standard solution, which is that is being added to the solution of unknown

concentration and its volume is measured.

Standard solution: a solution of precisely known concentration.

Standardization: using a standard to determine the concentration of another solution by

titration.

Equivalence point: The equivalence point occurs when stoichiometric equivalent amounts of

reactants have been consumed.

End point: The end of a titration reaction, often indicated by means of a dramatic color change.

(caused by a 3rd chemical added in small quantities to sample - indicator).

The color change for an acid/base reaction is due to excess amounts of acid or base present,

hence decreasing or increasing the pH.

The closer the equivalence point is to the endpoint, the more precise the results.

Fill in the following diagram with the correct terminology. Include a definition for each term.

A titration setup

Additional Titration Terminology

Equivalence point

Endpoint

Standardization

pH

Indicator

Titration Curve

Titration Steps:

A sample to be analyzed is measured in a small graduated cylinder or volumetric pipette and delivered to an Erlenmeyer flask.

A few drops of the appropriate indicator are added to the sample being analyzed.

After taking an initial reading of the volume of titrant in the burette, the titrant is added, slowly, to the sample in the Erlenmeyer flask, while the sample is swirled.

The endpoint of the titration occurs when the indicator colour changes dramatically. With a well-chosen indicator, the difference in the volumes of titrant required to reach the endpoint and the equivalence point should differ only by one drop of titrant (approximately 0.05 mL).

Lab 8C (sheet 8.3.4)

Page 315 questions

Sheet 8.3.3

TITRATIONS CURVES: A GRAPH OF pH vs. volume of titrant

The graph on the left shows the pH curve obtained when a strong base is added to a strong acid. The reaction mixture starts off very acidic and becomes very basic. The opposite is true when a strong acid is added to a strong base, as shown in the graph on the left.

There is a rapid change in pH as the equivalence point is reached. This is because the moles of the sample are being depleted and one drop of titrant can cause a large change in the pH.

Explain the graph below: (pick indicators)

Indicators Suitable for Strong Acid-Strong Base Titrations

Indicator pH range Colour change as pH increases

bromocresol green 3.8–5.4 yellow to blue

methyl red 4.8–6.0 red to yellow

chlorophenol red 5.2–6.8 yellow to red

bromothymol blue 6.0–7.6 yellow to blue

phenol red 6.6–8.0 yellow to red

phenolphthalein 8.2–10.0 colourless to pink

1. A titration is performed and the following pH curve is generated.(a) Select an indicator that would be

appropriate to use in this titration.

(b) What is the endpoint in this titration, given the indicator selected in part (a)?

(c) What is the equivalence point in this titration?

(d) What colour change would occur?

2. A titration is performed and the following pH curve is generated.

(a) Select an indicator that would be appropriate to use in this titration.

(b) What is the endpoint in this titration, given the indicator selected in part (a)?

(c) What is the equivalence point in this titration?

(d) What colour change would occur?

3. Why would bromocresol green be a poor indicator to use for either of these titrations?

Plotting a curve-sheet 8.3.7

Lab 8D if time (sheet 8.3.8)

8.3 review

Chapter review, test and unit test