Activity 7.8 (2 of 5) Student Handout (1 of 3)

Atomic Theory Lab PreLab: Define hydrate.

What is the formula of copper(ll) sulfate? _

Pre Lab -Coppet sulfate is bonded to water when in the crystal phase. This is called a hydrate. By simple heating, the

water molecules are liberated from the hydrate (they evaporate).

According to Proust's experimentation in the early 1800's, atoms combine in definite proportions by mass. This law can be extended to apply to molecules. In this instance, the same number of water molecules will be liber­ated from each copper sulfate molecule. The ratio of the amount of liberated water to the total mass of copper sul­fate and water should remain the same no matter what how much material is used.

1. Preliminary observations of copper (ll) sulfate pentahydrate crystals. Writing in complete sentences, record at least five qualitative observations. Make full use of available equipment including: microscope, balance, Bunsen burner. Draw two diagrams.

2. What substances from your everyday experience appear dry, but actually contain water? Work with your part­ner to compile a list of at least five substances. Give evidence to justify each claim.

Materials -­

• Scapula • Clay triangle • Iron ring • Burner • Balance'

• Watchglass • Ring stand • Evaporating dish • Tongs • Hydrate

Procedure Record all qualitative observations that seem relevant.

1. Record mass of evaporating dish and watch glass.

2. Add copper sulfate hydrate (CuS04) to an evaporating dish until it is approximately 05 em deep . Record mass of evaporating dish, watch glass and copper sulfate hydrate. Calculate the mass of the copper sulfate hydrate. Think: you need to determine the mass of the copper sulfateonly- no evaporating dish . How can you do this?

3. Place the evaporating dish on the clay triangle 5--6 em above the Bunsen burner the cooler part of the flame. Then place the watch glass on the evaporating dish. Heat the copper sulfate slowly. In heating, the copper sul­fate will gradually turn very pale blue or gray. If it begins to darken, you are heating it too fast, reduce the flame . If drc:p !e~ !:' ic.:::m Oil cool parts of the evaporating dish, heat them and they will disappear.

4. When all the copper sulfate has turned pale blue, allow evaporating dish to cool and then mass the evaporating dish and copper sulfate residue. Record.

5. Reheat evaporating dish for 3 more minutes and allow to cool. Mass dish and watch glass and record. If , masses are within .05 g, clean up your station . If not, repeat step five until the two subsequent mass readings are within .05 g of each other or time is called.

6. Obtlintheresults of the otIi~r lab groups and record.

Data Table Your tablewill resemble this one. You need to make one that fits all your data needs. If you need more heat­

ings, record those masses too. /

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Activity 7.8 (3 of 5) Student Handout (2of 3)

Mass of evaporatingdish, watch glass and hydrate

Mass of empty evaporatingdish and watch glass

Mass of hydratebefore heating

Mass of copper sulfateafter first heating

Mass of copper sulfateafter second heating

Mass of water evaporated

Ratio, by mass, of copper s

Ratio, by mass, of water to hydrate

Ratio, by moles, of copper sulfate to water

Ratio, by moles, of copper sulfate to hydrate

Ratio, by moles, of water to hydrate

Calculations

Show a complete set of calculations in order to complete the table above . Then show how you determined the

formula for the copper sulfate hydrate.

Analysis

Write a complete analysis. Answer the attached questions.

Paragraph 1: Purpose

What major concept in atomic theory was demonstrated in this lab? Hint: what are the atomic laws? Does this

lab support the law of multiple proportions, definite proportions or the law of conservation of mass? What was

your hypothesis? Was it supported or refuted?

Paragraph 2: Data Interpretation

What is your evidence to support the law this lab supports? Be specific.

What is the experimentally determined formula of this copper sulfate

hydrate?

Paragraph3:E"orAna~s~

Give two major sources of error in the data collection and how they /

affected the results? Explain your chain of reasoning for these results. How

could you reduce these major sources of error?

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Activity 7.8 (4 of 5) Student Handout (3 of 3)

Atoinic Theory Lab Discussion Questions 1. Why do we mass the evaporating dish and watch glass and then add the hydrate rather than zeroing the balance

with the glassware on the balance pan?

2. Does the change in color represent a physical or chemical change? Why?

3. Write the correct formula for your hydrate. Do the coefficients represent ratios of moles of hydrate to com­

pound or the ratios of masses of hydrate to compound?

4. What is the significance of heating the substance until two sets of masses are very close to each other?

5. How would your ratio of moles of water to moles of compound change if you did not actually evaporate all the

water from the hydrate? Explain your chain of reasoning.

6. What is the percent by mass of water in the formula for this hydrate? What is the percent by mass of oxygen?

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