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Explain in terms of particles and collisions how concentration, temperature and addition of a catalyst affect the rate of a reaction.

Concentration: the higher the concentration, the more particles in the same volume. The increase in particle numbers causes an increase in particle collisions, so the rate of reaction increases.Temperature: ...
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Answered by Emily W. • Chemistry tutor
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Guard cells open and close stoma in different conditions. When light intensity is high, potassium ions move into guard cells. Describe how this movement of potassium ions causes the stoma to open.

When the potassium ions move into the guard cells they increase the concentration. This causes water to move into the guard cells from more dilute areas by osmosis. The additional water leads to the guard ce...
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Answered by Emily W. • Biology tutor
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P is a point on a circle with the equation x^2 + y^2 = 45. P has x-coordinate 3 and is above the x axis. Work out the equation of the tangent to the circle at point P.

First insert x = 3 into the equation of the circle3^2 + y^2 = 459 + y^2 = 45 take 9 away from both sidesy^2 = 36 take the square root of both sidesy = 6 (not -6 as P is above the x-axis)Next find the gradien...
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Answered by Emily W. • Maths tutor
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Calculate the pH of a 0.0131 mol dm^-3 solution of calcium hydroxide at 10 degrees centigrade.

Multiply by 2 because calcium hydroxide = Ca(OH)2 so 2 x [OH-] per molecule.[OH-] = 0.0131 x 2 = 0.0262 Insert [OH-] value into the equilibrium equation along with the value of Kw at 10 degrees centigrade 2....
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Answered by Emily W. • Chemistry tutor
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Explain why adding small amounts of acid or base hardly changes the pH of an acidic buffer solution.

An acidic buffer solution is made up of a weak acid (e.g. ethanoic acid) and a salt containing its conjugate base (e.g. sodium ethanoate). It resists pH change via two mechanisms: The fact that the acid is w...
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