108. Solving a chemistry problem

For a suspension of amorphous silica SiO2 with a particle radius of 10 nm in an aqueous solution of sodium nitrate 5.00 cmol/l (pH = 4.5), an electrophoretic mobility of –1.34*10-8 m2*V-1*s-1 was reported. Calculate ξ-potential. Other required data: temperature 25 °C, viscosity 0.930 cP, er = 77.7.