With high concentrations the rate of reaction will be fast. This is because according to the collision theory the more you increase the concentration of a substance then the rate of collision increases.

With high concentrations there is more collision between the particles therefore they will react quickly and largely because the number of particles increase when the concentration is increased. Hence as the amount of solution is kept the same and only the concentration is varied, the time taken for the reaction to process will be shorter. Therefore the cross will disappear quickly. The cross will disappear quickly because when the concentration is increased the numbers particles are also increased causing more precipitate to form in a smaller length of time.

I have simplified my explanation in the diagram below to show the effect of concentration on particle activity.

As you can see the higher the concentration the more the particles are present and hence the more collision will take place in less time causing more precipitate to form in a short length of time.

Conclusion

After having analysed the graphs and the results I can say that as the concentration increases the rate of reaction becomes faster and the cross disappears quickly.

I can now give explanation for the conclusions for being as they are.

I have concluded that as the concentration increases the rate of reaction speeds up and the time taken for the cross to disappear becomes quicker. By my scientific knowledge and understanding I will explain why this is so.

When the concentration is increased there are more particles present for collision. Hence, more collision takes place. There are more particles to react with so the reaction becomes faster. When the reaction becomes faster the time taken for the sulphur precipitation to be formed becomes quicker. Therefore the cross disappears quickly. The rate of reaction increases because there are more particles that collide more often. This causes the rate of the reaction to increase. This is simplified in the diagram below.

With low concentrations there are less particles and less collision therefore the rate of the reaction is slow. With high concentrations there are more particles and more collision. Therefore the rate of the reaction is fast.