# Tutor profile: Sharine B.

## Questions

### Subject: Organic Chemistry

Electrophilic aromatic substitution is involved when anisole, toluene, chlorobenzene and nitrobenzene react with Br2. Arrange the given compounds in order of decreasing reaction rate.

In electrophilic aromatic substitution (EAS), - electron donating groups (EDG) speed up the reaction - electron withdrawing groups (EWG) slow down the reaction To answer the question, determine the substituent attached to benzene anisole: -OCH3 toluene: -CH3 chlorobenzene: -Cl nitrobenzene: -NO2 -OCH3 and -CH3 are electron donating groups so they speed up the reaction -Cl and -NO2 are electron withdrawing groups so they slow down the reaction Thus, reaction rate: anisole & toluene > chlorobenzene & nitrobenzene -OCH3 is a moderate activating group whereas -CH3 is a weak activating group so in terms of reaction rate: anisole > toluene -Cl is a weak deactivating group whereas -NO2 is a strong deactivating group so in terms of reaction rate: chlorobenzene > nitrobenzene Therefore, reaction rate: anisole > toluene > chlorobenzene > nitrobenzene.

### Subject: Chemistry

Which of the following indicators should be used if the pOH at the equivalence point is 6.3? Methyl orange: pKa = 3.4 Phenol red: pKa = 7.9 Phenolphthalein: pKa = 9.4

In titration, the appropriate indicator has a pKa value equal to or near the pH at the equivalence point. To answer the question, you need to solve the pH at the equivalence point using the given pOH, pH + pOH = 14 pH = 14 - pOH = 14 - 6.3 pH = 9.7 Since the pH at the equivalence point is 9.7, phenolphthalein, which has a pKa closest to 9.7, should be used.

### Subject: Algebra

A model rocket is shot upwards from the ground with an initial velocity of 64 feet per second. The formula h(t)=64t−16t^2 represents the rocket’s height off the ground in t seconds. How long does it take for the rocket to reach its maximum height?

Since the coefficient of t^2 is negative, h(t)=64t−16t^2 is an upside-down parabola. To get t, the time it takes for the rocket to reach its maximum height, you need to find the vertex (h,k) = (t, h(t)) of the upside-down parabola. h(t)= −16t^2 + 64t h(t)= at^2 + bt t = h = -b/2a = - (64)/(2)(-16) = 2 seconds Therefore, it takes 2 seconds after being tossed up to reach its maximum height.

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