Topscore test 2 chem question 68
Started by dental881
Is it multiple choice?
Since the molarities are the same, if you added 20 ml of HCl you'd have a solution with a pH of 7.
Since 1 M HCl has a pH of 0 though (100 times more H3O+ than pH 2), you don't want to add much more than that.
If they actually want you to calculate it out instead of just estimating the obvious answer choice, just be aware that the HCl and NaOH "cancel out" since it's a neutralization, and then find the H3O+ concentration only factoring in the extra acid (0.4 ml). In this case working backwards from a plausible answer is much faster than working forwards to an unknown solution.
Since the molarities are the same, if you added 20 ml of HCl you'd have a solution with a pH of 7.
Since 1 M HCl has a pH of 0 though (100 times more H3O+ than pH 2), you don't want to add much more than that.
If they actually want you to calculate it out instead of just estimating the obvious answer choice, just be aware that the HCl and NaOH "cancel out" since it's a neutralization, and then find the H3O+ concentration only factoring in the extra acid (0.4 ml). In this case working backwards from a plausible answer is much faster than working forwards to an unknown solution.
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Okay i just worked through topscores disgusting explanation. We know that we half to add at least 20ml to get the pH around 7. So total volume is 40+x. x is the amount of HCl were looking for. So now we set up M1V1=M2V2. (1M of HCl)(x mL)=(.01M[we get this from the pH=2, bc log of .01 = 2])(40+x mL). so its (1)x=(.01)(40+x), now solve for x. x=.4mL and thus the final amount is 40.4mL. To get just HCl mL subtract the 20mL of NaOH, leaving you with 20.4mL. I hope that helped!
an additional ten would give you 50 ml of solution. Solve for moles of H+ and divide by TOTAL liters for the new concentration.
