The Effect of Hydrochloric Acid on the Rate of Reaction

The Effect of Hydrochloric Acid on the Rate of Reaction

Sodium thiosulphate + hydrochloric acid ―› sodium chloride + sulphur +

water + sulphur dioxide

Na S O + 2HCl ―› 2NaCl + F + H2o + SO2

Preliminary Investigation:

Before we carried out our investigation in full, we needed to do some

preliminary work to prove that the variables we were changing were

suitable, the concentrations of hydrochloric acid would not take too

long or short a time and to discover what range of values would be

needed on apparatus such as the conical flask. The results of our

preliminary work were as follows:

Concentration (%)

Time taken for cross to disappear (secs)

80

121

50

133

20

153

We also realised that we needed to use 25 ml of each sodium

thiosulphate and hydrochloric acid to make 50 ml. This seemed like an

appropriate amount to work with as it would offer significant results

without being over-large. Although we were only using 50 ml of

chemicals, we decided to use a 100ml conical flask. This allowed room

for reactions to take place without it spilling over. To change the

volume of our eventual solution, we would use a measuring cylinder to

measure the appropriate volumes of each, and we would not re-use the

solutions as once they had been reacted they could not be re-reacted.

The thermometer we used ranged from -10 to 110 degrees Celsius.

Although if this experiment is done correctly the temperature should

not change, we must make allowances for if it does, and that entails

allowing for negative temperatures. We chose a thermometer that was

accurate to 1 degree Celsius as we needed only that level of accuracy,

no more. We used a 25ml measuring cylinder as that was the maximum

amount we would be measuring out each time. It was accurate to 0.5 ml.

We are intending to repeat this experiment several times in order to

gain accurate, conclusive results.