Disappearing Cross
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THE EFFECT OF CONCENTRATION ON REACTION RATE
INTRODUCTION
Concentration describes how much of a particular substance there is in a specific volume of solution. □ A dilute solution has only a little of the substance in a lot of water. □ A concentrated solution has a lot of the substance in less water.
If we take 100cm3 beakers of dilute acid and concentrated acid, there will be fewer acid particles in the beaker of dilute acid than in the beaker with concentrated acid, even though the volumes of the two solutions are the same. In chemistry, we count particles in terms of formula masses, so we describe concentration in terms of the number of formula masses (moles) of the substance there are in every cubic decimetre (litre) of solution, written as moles.dm-3 or M for short.
USING A 'CLOCK REACTION' TO MEASURE RATE
A 'clock reaction' is a bit like a race. In a race the competitors are timed over a fixed distance. The shorter the time, the quicker the competitor ran. In a chemical reaction we can time how long it takes for a fixed amount of reaction to take place. Again, the shorter the time, the quicker the reaction, and so the faster the rate.
Speed = fixed distance so Reaction rate = fixed amount of reaction time taken time taken
From this we can see that the reaction rate is proportional to l ÷ time.
THE DISAPPEARING CROSS
The reaction used in this experiment is between dilute hydrochloric acid and sodium thiosulphate (formula Na2S2O3). You can see from the chemical equation below that one of the products is sulphur, which does not dissolve in water.
[pic]
As the reaction proceeds, a fine precipitate of sulphur forms, which makes the water go cloudy. If the reaction is carried out in a beaker standing on a piece of paper marked with an X, the precipitate eventually becomes thick enough to stop the X from being seen. We can time how long it takes for the X to disappear for different concentrations of
THE EFFECT OF CONCENTRATION ON REACTION RATE
INTRODUCTION
Concentration describes how much of a particular substance there is in a specific volume of solution. □ A dilute solution has only a little of the substance in a lot of water. □ A concentrated solution has a lot of the substance in less water.
If we take 100cm3 beakers of dilute acid and concentrated acid, there will be fewer acid particles in the beaker of dilute acid than in the beaker with concentrated acid, even though the volumes of the two solutions are the same. In chemistry, we count particles in terms of formula masses, so we describe concentration in terms of the number of formula masses (moles) of the substance there are in every cubic decimetre (litre) of solution, written as moles.dm-3 or M for short.
USING A 'CLOCK REACTION' TO MEASURE RATE
A 'clock reaction' is a bit like a race. In a race the competitors are timed over a fixed distance. The shorter the time, the quicker the competitor ran. In a chemical reaction we can time how long it takes for a fixed amount of reaction to take place. Again, the shorter the time, the quicker the reaction, and so the faster the rate.
Speed = fixed distance so Reaction rate = fixed amount of reaction time taken time taken
From this we can see that the reaction rate is proportional to l ÷ time.
THE DISAPPEARING CROSS
The reaction used in this experiment is between dilute hydrochloric acid and sodium thiosulphate (formula Na2S2O3). You can see from the chemical equation below that one of the products is sulphur, which does not dissolve in water.
[pic]
As the reaction proceeds, a fine precipitate of sulphur forms, which makes the water go cloudy. If the reaction is carried out in a beaker standing on a piece of paper marked with an X, the precipitate eventually becomes thick enough to stop the X from being seen. We can time how long it takes for the X to disappear for different concentrations of