Ion Exchange and Electrophoretic Separations · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Sorting charged species by charge

Science · Chemistry · ages 20-21
Name ______________________   Date ____________

  1. How are bound ions released from an ion exchange column?

    • By heating the column until the resin melts
    • By washing with a competing ion through extra salt or a pH shift
    • By shaking the column until the beads break apart

  2. A cation exchanger carries negative resin beads. Which ions will it hold?

    • Positive ions, since opposite charges grip
    • Negative ions, since like charges grip
    • Neutral molecules, since charge never matters

  3. In electrophoresis, small highly charged molecules travel faster than big lightly charged ones.

    Circle one:   True   False

  4. Why does SDS PAGE separate proteins almost purely by size?

    • SDS unfolds proteins and coats them evenly negative, so only size is left to matter
    • SDS gives every protein the same shape and removes all charge
    • SDS sorts proteins by colour, which tracks size exactly

  5. A weak acid sits at a pH where it loses its proton. How does its retention on an anion exchanger change?

    • It washes straight through, since protons destroy all binding
    • It binds to the cation exchanger instead, since acids are always positive
    • It binds more strongly, since it has turned negative

  6. Short DNA fragments outrun long ones toward the positive electrode. Why?

    • Short fragments carry positive charge while long ones carry negative charge
    • Every fragment carries similar charge per mass, so the mesh tangles long pieces while short ones slip through
    • The electrode attracts short fragments and repels long ones

  7. A conductivity detector sees nothing but eluent background. What does the suppressor change?

    • It lowers the background signal of the eluent so analyte peaks stand out
    • It raises the eluent signal so peaks grow taller
    • It removes the analyte so only eluent remains

  8. At pH 6, which amino acids bind a cation exchanger, and which way does each travel in electrophoresis?

    • All amino acids bind whatever the charge, and all travel the same way
    • Only the negatively charged ones bind the negative beads, and each species runs toward its matching electrode
    • Only the positively charged ones bind the negative beads, and each species runs toward its opposite electrode
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Sorting charged species by charge W1-mt_6xaiivXbAd-s1

  1. By washing with a competing ion through extra salt or a pH shift · The competitor disrupts the electrostatic grip and takes the binding spots.
  2. Positive ions, since opposite charges grip · The resin keeps what carries the opposite charge and lets the rest wash through.
  3. True · Size, shape, and net charge together set the speed through the gel.
  4. SDS unfolds proteins and coats them evenly negative, so only size is left to matter · Uniform charge per mass cancels the charge variable, leaving the gel mesh to sort by size.
  5. It binds more strongly, since it has turned negative · Losing the proton creates a negative ion, which is exactly what the positive beads grip.
  6. Every fragment carries similar charge per mass, so the mesh tangles long pieces while short ones slip through · Charge per mass is nearly equal, so the gel mesh does the sorting by length.
  7. It lowers the background signal of the eluent so analyte peaks stand out · Cutting the background is what makes conductivity detection of the peaks possible.
  8. Only the positively charged ones bind the negative beads, and each species runs toward its opposite electrode · Binding needs opposite charges, and motion always heads toward the oppositely charged electrode.
Worksheet · LightMySky