The pH of a solution is 2.55. What is the [H3O+]?

pH = 4

Explanation:

To calculate the pH of a solution, use the equation p H = − log [ H 3 O + ] Since we are given the hydronium ion ( H 3 O + ) concentration of the solution, we can plug this value into the formula. p H = − log [ 1.00 × 10 − 4 M ]  p H = 4 The pH of this solution is 4. Added notes: p H = p H 3 O +  because hydrogen ions attach to water molecules for form hydronium ions. Some other key things to remember for pH calculations include: pH + pOH = 14 pH = -log[ H + ]  pOH = -log[ O H − ] [ H + ] = 10 − p H  [ O H − ] = 10 − p O H

answer: c.

explanation:

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol