Marble chips

How do different concentrations of hydrochloric acid affect mass of marble chips?

In my preliminary coursework the experiment I chose to investigate was how of the concentration of hydrochloric acid affects the rate of reaction with magnesium strips. I was interested to see what type of gas is produced and if there was a change in mass in the magnesium strips. After completing this experiment, I noticed that there was a decrease in mass which matched my prediction. However there wasn't much variation in my results, so I decided to change the reactant for my main experiment from magnesium strips to marble chips. This is because the magnesium strips completely dissolved in the 2 molar and 1.8 molar solutions completely, this means that these experiments weren't reacting the whole amount of time, for that reason not producing accurate results. I am therefore choosing marble chips as my reactant for my main experiment as they have a slower reaction rate and I feel that they would produce a wider variation of results.

Possible factors that might affect my experiment:

· The ratio of the surface area of the marble chips to the mass. This might affect my results because the marble chips (calcium carbonate) have a smaller surface area in comparison to compare to calcium carbonate powder, meaning that the reaction with the marble chips will be slower than a powdered solid because it has a smaller surface area meaning that there less collision between the acid and the marble chips.

· The temperature, this is because if the hydrochloric acid has a higher temperature, the collision of the particles will be much greater because there is an increase in energy, which will speed up the reaction between the marble chips and the hydrochloric acid.

· The concentration of the acid. This would affect my results as if there is a higher concentration of acid, there would be more collision between the acid and the marble chips. Theoretically this would mean the higher the concentration of acid, the bigger the loss in mass due to the more vigorous reaction.

My Chosen Factor:

The factor I am choosing to investigate is to see what affect the concentration of hydrochloric acid has on the loss in mass of the calcium carbonate (marble chips). I decided to focus on this as I could use a wide range of concentrations of acid in this experiment and it will be interesting to see what affect different concentrations have on the mass of the marble chips and if there is a trend between my results.

Aim: The aim of this experiment is to see what effect different concentrations of hydrochloric affect the change in mass in marble chips.

Variables:

The controlled variables in my experiment were: The time in which the marble chips were submerged in the hydrochloric acid, the original mass of the marble chips, the size of the marble chips and the same volume of the solutions in which the marble chips were being submerged.

The Independent variable in my experiment was: The molar concentration of the hydrochloric acid.

The dependant variable in my experiment was: The final mass of the marble chips after being submerged in the concentrations of hydrochloric acid.

Introduction and scientific explanation:

In my experiment the factor I chose to measure was the effect of different concentrations of hydrochloric acid on the change in mass in marble chips. I decided to use different concentrations of hydrochloric acid (0, 0.4, 0.8, 1.2, 1.6 and two molars) as this range enabled me to gather a greater idea on what effect these concentrations had on the change in mass. I used 0 molars (water) as a control in my experiment. I feel that the higher the concentration of hydrochloric acid the larger the loss in mass in the marble chip. This is due to collision theory. Collision theory is the idea that the higher the concentration of acid, the more acid molecules within the solution, meaning more collisions can take place in a reaction, making the reaction speed up resulting in a larger mass loss in the calcium carbonate chips.

Apparatus:

· Conical flask - I decided to use this as it was an easy and useful to carry out the test in.

· Cotton wool - this was used as a bung at the top of the conical flask so the gas produced could still escape. The cotton wool also prevents the experiment spitting.

· Measuring scales - I decided to use this as it is an accurate way of measuring the mass of something.

· Measuring cylinder - I decided to use this as it is an accurate way of measuring out the different concentrations of the hydrochloric acid.

· Stopwatch - I decided to use this as it is an accurate way of timing my experiment.

Safety:

To make sure I was safe in this experiment, I had to take the right precautions. I made sure my bag was under the table, as this would stop anybody from tripping over, preventing spillage of acid. I also made sure my hair was tied back from my face as this made sure that my full attention was on the experiment. I also wore a lab coat and safety glasses as this stopped any acid spilling or me or spitting up in my eyes. After I had finished the experiment, I put the reacting chemicals in the fume cupboard so the lab technicians could deal with the chemicals safely.

Method:

1. Weigh out 5 lots of marble chips, each weighing 5g.

2. Use a measuring cylinder to measure out the different concentrations of hydrochloric acid (0, 0.4, 0.8, 1.2, 1.6 and 2 molars).

· 0 molars of hydrochloric acid is 100ml of H20.

· 0.4 molars of hydrochloric acid is 20ml of 2mol / dm³ of hydrochloric acid + 80ml of H20.

· 0.8 molars of hydrochloric acid is 40ml of 2mol / dm³ of hydrochloric acid + 60ml of H20.

· 1.2 molars of hydrochloric acid is 60ml of 2mol / dm³ of hydrochloric acid + 40ml of H20.

· 1.6 molars of hydrochloric acid is 80ml of 2mol / dm³ of hydrochloric acid + 20ml of H20.

· 2 molars of hydrochloric acid is 100ml of 2mol / dm³ of hydrochloric acid.

3. Place the conical flask on the scales and turn them on.

4. Add the first concentration of the hydrochloric acid in the conical flask.

5. Add the first 5g set of marble chips, making sure the stop watch is started as soon as the marble chips come in contact with the hydrochloric acid.

6. Quickly place the cotton wool bung in the opening of the conical flask, as this will prevent the acid spitting out of the top.

7. Record the change in mass every 20 seconds for two minutes in a results table.

8. Repeat the experiment for each solution.

Equation:

The equation below shows the reaction which occurred in my experiment:

CaCO3(s) + 2H+ (aq) à Ca+ + (aq) + H2O + CO2 (g)

Table of results:

I did this experiment twice as this ensured that my results are more accurate, below are my tables of results:

Table of Results Experiment 1:

Concentration of Hydrochloric acid (molars)

(Starting mass) 0 seconds

20 seconds

40 seconds

60 seconds

80 seconds

100 seconds

(finishing mass) 120 seconds

(g)

(g)

(g)

(g)

(g)

(g)

(g)

2

99.520

99.513

99.462

99.409

99.347

99.264

99.180

1.6

105.145

105.126

105.103

105.067

105.030

104.975

104.926

1.2

102.710

102.710

102.700

102.690

102.670

102.660

102.640

0.8

102.400

102.410

102.400

102.400

102.390

102.380

102.370

0.4

96.640

96.640

96.640

96.640

96.630

96.630

96.630

0

106.200

106.200

106.190

106.200

106.200

106.200

106.200

Table of Results Experiment 2:

Concentration of Hydrochloric acid (molars)

(Starting mass) 0 seconds

20 seconds

40 seconds

60 seconds

80 seconds

100 seconds

(finishing mass) 120 seconds

(g)

(g)

(g)

(g)

(g)

(g)

(g)

2

236.700

236.680

236.650

236.610

236.550

236.490

236.430

1.6

239.570

239.550

239.530

239.500

239.460

239.420

239.370

1.2

233.740

233.740

233.730

233.710

233.690

233.670

233.640

0.8

232.960

232.950

232.940

232.940

232.920

232.920

232.910

0.4

230.980

230.970

230.970

230.970

230.960

230.960

230.950

0

231.790

231.780

231.780

231.770

231.770

231.770

231.770

Resulting Mass Change:

Concentration of Hydrochloric Acid (molar)

Change in Mass (g) in Experiment 1

Change in Mass (g) in Experiment 2

Average change in mass (g)

Rate of reaction (g/m)

2

0.340

0.270

0.305

0.153

1.6

0.219

0.200

0.210

0.105

1.2

0.070

0.100

0.085

0.043

0.8

0.030

0.050

0.040

0.020

0.4

0.010

0.030

0.020

0.010

0

0.000

0.020

0.010

0.005

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