Table 1.

Central composite design (CCD) for optimizing temperature and pH with experimental data and model prediction.

No. of runs	Temperature (x1) coded level	pH (x2) coded level	Temperature actual level	pH actual level	CaCO3 precipitate (g)
					Experimental data	Model prediction	Error (%)
1	0	−1.4142	29	6.37	3.29	2.25	31.64
2	1.41421	0	35	8.5	18.62	15.22	18.28
3	1	1	33	10	16.9	20.35	20.40
4	−1	1	25	10	11.28	12.43	10.17
5	−1.41421	0	23	8.5	4.91	4.76	3.07
6	1	−1	33	7	10.91	13.32	22.06
7	0	0	29	8.5	6.6	6.60	0.00
8	0	0	29	8.5	6.7	6.60	1.49
9	−1	−1	25	7	6.34	6.45	1.68
10	0	1.41421	29	10.62	27.3	24.79	9.20