CHE 1220 Lecture Notes - Lecture 9: Molar Mass, Aluminium Sulfate, Empirical Formula

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lilacsardine521

21 Feb 2017

School

St. John's University

Department

Chemistry

Course

CHE 1220

Professor

Eranda Maligaspe

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Document Summary

For addition and subtraction, the answer should have the same number of decimal places as the quantity with the fewest number of decimal places. For multiplication and division, the number of significant figures in the answer should not be greater than the number of significant figures in the least precise measurement. Exact numbers, which come from definitions such as 12 in. 1 mole = 6. 022 1023 items = avogadro"s number = na grams. Model 3: determination of molecular formulas of % mass an element of mass element the present ain sample of mass total sample the. Empirical formula = formula with smallest whole number ratio of atoms of different elements in compound. Molecular formula = some whole number multiple of the empirical formula. Requires molar mass to determine molecular formula from empirical formula: given masses of each element present in a sample, convert mass of each element to moles of each element.

Part I: What is the complete formula (Salt · x H2O) for the hydrate you will be given in lab?

(25 points)

General Procedural guidelines for this lab:

From the very beginning of this experiment, only handle the crucible or evaporating dish with crucible tongs. SAFETY: The crucible will be very hot! Never touch the crucible while it could be hot. Use crucible tongs.
Use the same scale throughout this lab.
Do all of your calculations with proper sig figs.
For additions and subtractions, keep the fewest number of decimal places.
For multiplication and division keep the fewest number of significant figures.
While things are heating and cooling, work on Part II of this task.

Procedure: Watch this video, read along with the following procedure, and take notes: https://www.youtube.com/watch?v=k2s-YG15eIA

Wash out a crucible and flame dry. Heat the crucible with a Bunsen burner for 5 minutes on high and let it cool for 10 minutes.

Zero the balance.
Mass the crucible and record the mass (with units). __________

Fill the crucible about ¾ full with the hydrate.

Mass the crucible with the hydrate and record this mass. __________

Record the color of the hydrate (before heating). __________

Heat the crucible with the until all water is driven off. What is left in the crucible is the anhydrate.

Record the color of the anhydrate (after heating). __________

Let the crucible cool for a few minutes (at least 10). Then mass the anhydrate and crucible and

record this mass. __________

Complete the calculations to determine the (i) % mass of water in the hydrate and (ii) the value for x for your hydrate. Show all of your calculations. The calculations for the % mass of water in the hydrate are outlined in the video. You will have to do the calculations for x by yourself. Show all of your calculations on this page or another page.

MAKE A DATA TABLE HERE FOR ALL OF YOUR DATA:

MAKE A RESULTS TABLE HERE FOR THE RESULTS OF YOUR CALCULATIONS:

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CHE 1220 Lecture Notes - Lecture 9: Molar Mass, Aluminium Sulfate, Empirical Formula

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Related Questions

Part I: What is the complete formula (Salt · x H2O) for the hydrate you will be given in lab?

(25 points)