Question

A1. Determine the concentration of the dissolved B₄O₅(OH)₄^2– in each sample titrated; show a complete calculation for beaker #1.

A2. Calculate K_sp for each borax solution.

A3. Prepare a graph of your results, plotting the two quantities x and y (as defined in the introduction). Label everything clearly! Draw a best fitted line.

A4. Using y=mx+b of your best fitted line, calculate DH° and DS° for this reaction. Make sure to keep track of units, especially for R, so that the units of DH° and DS° work out sensibly.

Q1) What would happen to experimental Ksp if the buret was contaminated with other acids?

My results :

amount of borax: 25.004g

concentration of HCl : 0.2150M

temperature	31.5C	24.9C
initial point of HCl	0.00ml	0.00ml
final point of HCl	18.3ml	12.5ml

All gruop info.

Group #	Experiment	mL of Borax	T (in C)	mL of HCl (0.2150M)	Unusual Qual Observation
1	1	5.90	55.00	43.50	yellow => pink
	2	5.50	47.30	36.10	yellow => pink
2	1	5.20	48.00	29.30	Yellow --> Pink
	2	5.15	24.00	16.70	Yellow --> Pink
3	1	5.00	50.30	53.11	lemon yellow to pale peach
	2	5.00	23.10	13.71	lemon yellow to pale peach
4	1	5.00	27.50	13.80	Yellow -->bright pink
	2	5.00	15.00	16.30	Yellow --> Bright pink
5	1	5.00	47.50	47.60	Yellow -> Peach coloration
	2	5.00	41.50	31.70	Yellow -> Pink
6	1	5.00	47.00	30.00	yellow to bold pink
	2	5.00	39.10	25.26	"               "
7	1	5.00	31.50	18.30	Yellow to Pink
	2	5.00	24.90	12.50	Yellow to Peach
8	1	5.00	48.00	43.60	yellow -> pink
	2	5.00	41.00	35.90	yellow -> salmon colored

Answer 1

The relationship between free energy (ΔG), enthalpy (ΔH), entropy (ΔS) and the equilibrium constant (K) for a chemical reaction at a specific temperature (T), is shown in the equation below. The Gas Constant, R, is equal to 8.314 J/mol·K

If we rearrange the first equation we get

Note that equation resembles the point-slope form of a line(y = mx + b). A plot of ln K versus (1/T) should result in a straight line with a slope equal to (–ΔH°/R) and a y-axis intercept equal to (ΔS°/R). Enthalpy, ΔH, is determined from the slope. To calculate entropy, ΔS, plug the value just found for ΔH into the equation and solve using a data point.

The procedure is:

1-. Calculate the concentration of borate ion for each titration. Use the borate ion concentration to determine Ksp at each temperature. Convert Celsius temperatures to inverse Kelvin temperatures (1/T) and summarize your data and calculated values in a table with 5 columns: T(K), 1/T(K-1), [borate ion], Ksp, and ln (Ksp).

Plot ln Kspvs 1/T(Kelvin). Clearly, display the equation and the R² value on the plot. If the R² value falls below 0.90, remove the data point that appears to be the outlier and replot. (Both plots, with and without the outlier, should be turned in.) Determine ΔH (kJ/mol) and ΔS (J/mol-K) from the plot’s equation.

DH =-25561.9 J

DS=3641.39 J

DG=-1187711 J

The concentration of the acid could change and react