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Explain the trend in boiling points between HF, HCl and HBr.

There are two themes in this answer. The first being the hydrogen bonding potential of HF and the second being the difference in size of the of the halide ions. Fluorine is one of three elements that can for...
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Answered by Thomas S. • Chemistry tutor
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In a sentence like "La tarte que j'ai faite", why does the past participle match the gender of the preceding subject noun?

In French sentences, when the past participle comes after the subject noun, it always matches the gender and the number of the subject noun. For example, in "Les rendez-vous qu'on a oubliés", the p...
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Answered by Benedek B. • French tutor
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How much time should I spend planning an essay in an exam?

As a general rule, longer than you think! Planning is often overlooked but it is essential for consistent, high-level answers: perfect your planning and you'll be set to give your best possible answer. For a...
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Answered by James W. • History tutor
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The curve C has the equation: 2(x^2)y + 2x + 4y – cos (πy) = 17 use implicit differentiation to find dy/dx in terms of x and y

Using the product rule: d/dx(ab)=ab’ + a’b where a and b are variables which have been differentiated with respect to x Derivative: 2(x^2(dy/dx)+2xy) + 2 + 4dy/dx+πsin(πy)dy/dx=0 Expand brackets: 2x^2(dy/dx)...
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Answered by George G. • Maths tutor
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A 4 digit number is picked. It's second digit is a prime number, it must be even and it must be greater than 5000. How many possible numbers can be picked?

This involves the product rule for counting. Step 1: Identify the possible numbers for the first digit 5, 6, 7, 8 or 9 (5 in total) Step 2: Identify the possible numbers for the second digit 2, 3, 5 or 7 (4 ...
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Answered by Thomas S. • Maths tutor
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