(* the data *)
aciddata  :=  
        List[{0.00001,  4.70},  {0.00005,  4},  {0.0001,  
            3.70},  {0.0006,  2.92},  {0.0008,  2.80}, {0.001,  
            2.7}]

(* the plot of the data *)
p1  =  
        ListPlot[aciddata,  
          PlotStyle -> {PointSize[0.02],  RGBColor[1, 0, 0]},  
          PlotRange -> {{0,  0.0015},  {2,  4.8}},  
          PlotLabel ->  "pH vs. Concentration",  
          AxesLabel -> {"Concentration (M)", "pH"},  
          TextStyle -> {FontSize -> 18}]

(* fit the data to a model of the form P[M_] L = 
            A  +  B*Log[M] *)
Solve[{
A  +  
              B*Log[0.00001] == 
            4.70, 
A  +  B*Log[0.00005] == 
            4
},  {A,  B}]

(* the model *)

P[M_] :=  -0.3073679532568737`  -  
        0.4349344541917281`*Log[M]
p2 = 
      Plot[P[M],  {M,  0,  
          0.0015},   PlotRange -> {{0,  0.0015},  {2,  
              4.8}}]

(* the model along with the data *)

Show[p1,  p2]

(* approximate the rate of change at M  =  0.00001 *)
(P[0.00001  +  0.01]  -  P[0.00001])/
        0.01

(P[0.00001  +  0.001]  -  P[0.00001])/0.001

(P[0.00001  +  0.0001]  -  P[0.00001])/0.0001

(P[0.00001  +  0.00001]  -  P[0.00001])/0.00001

(P[0.00001  +  0.0000001]  -  P[0.00001])/0.0000001

(P[0.00001  +  0.0000000001]  -  P[0.00001])/
      0.0000000001

(* 
        this is likely getting close to a reasonable approximation *)

(* Rate of change data *)
acidratedata  :=  
        List[{0.00001,  -43429.4},  {0.00005,  -8685.9},  {0.0001,  -4342.9},  {0.0006,  -723.8},  {0.0008,  -542.868}, {0.001, -434.3}]

(* plot of the rates of change *)
p3 = ListPlot[
          acidratedata,  
          PlotStyle -> {PointSize[0.02],  RGBColor[1, 0, 0]},  
          PlotRange -> {{0,  0.0015},  {-50000,  0}},  
          PlotLabel ->  "pH Rate of Change",  
          AxesLabel -> {"Concentration (M)", "pH/M"},  
          TextStyle -> {FontSize -> 
                18}]

(* the rate model along with the data-- - 
            although they will have no way of determining this model *)

Show[p3,  
      Plot[-1/(Log[10]*M),  {M,  0,  0.0015}]]