Activity 01 Finding the Relative Atomic Mass of an Unknowm Metal by Gas Collection

Student Worksheet

 Ac t iv it y 1: Fin di ng th e rel ati ve at om i c m ass of an u nk no wn met al b y g as c ol lec ti on Objective Be able to collect a gas from a reaction. Be able to measure the volume of a gas. Be able to calculate relative atomic mass. • • •

Equipment/materials  –3   1.00 moldm  hydrochloric acid, HCl Weighing bottle Unknown metal, X   Spatula Conical flask Delivery tube 3   250cm  measuring cylinder    Bowl Mass balance 3   25cm  measuring cylinder  Stand and clamp • • • • •

Safety Wear eye protection. Unknown metal is flammable. Hydrogen gas is flammable. No naked flames

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Highly flammable

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Procedure 1. Set up your apparatus as shown in the diagram. You must fill the measuring cylinder with water, cover the open end and place this under water in the bowl provided. 2. Place between 0.15g and 0.20g of the unknown metal in the conical flask. 3 3. Measure out 25.0cm  hydrochloric acid (HCl) and add this directly to the conical flask as quickly as possible, connecting the delivery tube to the flask immediately afterwards. 4. Ensure that all of the metal has reacted. 5. Collect the gas and record the final volume of hydrogen.

Diagram

Data 3 Molar gas volume is 24000cm  at 298K and 101kPa (RTP) Equation for reaction:

X + 2HCl

XCl2 + H2

 An aly si s o f r esu lt s Calculate the amount, in mol, of hydrogen collected. Calculate the amount, in mol, of unknown metal, X, used. Calculate the relative atomic mass, A mass, Ar , of X. Suggest an identity for X based on your value of A  Ar  and its observed reactivity. •

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From th e examiner… examiner… Record your weighings and gas volume measurement before you before  you begin your calculations. Explain each line of your calculation as shown in the  Analysis of Results Results section  section above. Consider how many significant figures to use within the calculation. Consider how many significant figures to use in your final answer. •

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Questions 1. State a major procedural error for this experiment. 2. Suggest a modification which which would reduce this major procedural error. 3. Calculate amounts in moles (using your value of A of Ar for X) to show that the acid was in excess. 4. How would you modify the procedure if metal X was provided in lump form? 5. How could this experiment be modified to find the relative atomic mass of lithium?

Practical activities have been checked for health and safety advice by CLEAPSS. All users will need to review the risk assessment information and may need to adapt it to local circumstances.

© Pearson Education Ltd 2008 This document may have been altered from the original

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