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The mass of a balloon is 0.02g before it is filled with air. After it is blown up with air the mass is 0.04g. Assuming oxygen makes up 21% of air, calculate the number of moles of oxygen in the balloon.

Mass of oxygen in balloon = 0.02 x 0.21 Mr (O2) = 16 x 2 = 32 Moles = mass / Mr = (0.02 x 0.21) / 32 = 1.31 x 10^4 moles Or 0.000131 moles
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Answered by Alice W. • Science tutor
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Explain how atherosclerosis develops and how it leads to coronary heart disease (8)

-Atherosclerosis: hardening of blood vessels (specifically those that withstand high blood pressure, ie arteries.) Blood vessels are composed of three layers: the tunica intima, tunica media and tunica adven...
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Answered by Iliana M. • Biology tutor
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How should I approach material that I haven't seen before in an exam?

Firstly, it is important to be familiar with the mark scheme in assuring that you know exactly what is expected of you during this examination. It would also be good to establish where you fit within this ma...
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When do you use 'avoir' and 'être' when using 'Le passé composé'?

To form 'le passé composé' (the perfect tense), you need to use an auxiliary verb which is either avoir or être plus the past participle. Avoir is usually used but when the verb is a verb of motion or a refl...
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Answered by Amelia H. • French tutor
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How do I factorise a quadratic equation?

A quadratic equation is one that takes the form.. ax 2 + bx +c = 0 Factorising an equation like this involves putting the equation into two brackets. The method varies slightly dependent on whether a = 1 or ...
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Answered by Beth E. • Maths tutor
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