TA: - This exercise is due at 12:00 when you come to lab. 1) How many ions are f

Question

TA: - This exercise is due at 12:00 when you come to lab. 1) How many ions are formed for each formula unit of sodium borate (borax) that dissolves in water? The equation below is derived in the lab manual. It shows how the equilibrium constant of a chemical reaction is related to the temperature (in Kelvins) 2) In(K RTR In the experiment you will be determine the equilibrium constant for a reaction at several different temperatures. What quantities should be plotted on the y-axis and x-axis in order to obtain a straight line with a slope equal to -AH/R? x-axis quantity y-axis quantity Based on the equation above, suppose the equilibrium constant for a reaction gets smaller at higher temperatures. In this case, would the reaction be endothermic or exothermic? for your answer. 3) Explain your reasoning

Explanation / Answer

Na2B4O7 + 7H2O -----> 2NaOH + 4H3BO3 ( Boric acid)

NaOH ------>Na++OH-

H3BO3--->3H++ BO3-3

so total no of ions are 2*(1+1) for NaOH and 4*(3+1) H3BO3

4+16= 20 ions in total when Borax is dissolved in water.

2. the equation given is lnK= -deltaH/RT+ deltaS/R

so a plot of lnK vs 1/T gives straight line whose slope is -deltaH/R and intercept is deltaS/R

so x axis is 1/T ( T has to be in K) and y axis is lnK

3. When temperature is increased, if the equilibrium constant gets smaller, this suggests that deltaH is -ve. -deltaH/RT gets reduced. So lnK gets reduced. So the reaction is enxothermic.

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