1. In a small container, dissolve 0.5 goftable salt (NaCl in 10 mLof distilled w
ID: 515808 • Letter: 1
Question
1. In a small container, dissolve 0.5 goftable salt (NaCl in 10 mLof distilled water to make a -1 M solution. 2. In a small container, dissolve 2 g of table sugar (sucrose) in 10 mL of distilled water to make a-1 M solution. ass vials or clear, colorless plastic cups, place 3 mL of the gold 3. Into each of four gl nanoparticle solution you prepared in Part A. Add 3 ml distilled water to each vial Left: A micrograph of 13 nm-diam 4. With a dropper, add 5-10 drops, one at a time, of the salt solution from part B, eter Au nanoparticles. Right: An step 1 to one of the vials. Record your observations. (Refer to an unused solution illustration an Au nanoparticle sur- face. Each nanoparticle is made for comparison.) What is happening to the nanoparticles in solution? of many (more than 500,000) Au 5. With a dropper, add 5-10 drops, one at a time, of the sugar solution from part B atoms. Citrate anions cover the step 2 to one of the vials containing fresh nanoparticle solution. Record your nanoparticle surface observations. (Refer to an unused solution for comparison.) 6. Choose another substance to add to a third vial. One suggestion is a household liquid such as vinegar. Check with your instructor about your choice. Before adding the substance, predict whether or not a color change will occur. Det Is the Quest ens Questions EXP 1. Based fact that the citrate anions cover the surface of each nanoparticle, explain what keeps the nanoparticles on the from sticking together gregating in the original solution. 2. Why does adding the salt solution produce a different result from adding the sugar solution? 3. How could the effect in part B be used to detect the binding of biomolecules, such as DNA or antibodies, that stick to one another or to other molecules? How could these molecules be used to cause aggregation of the nanoparticles? Information from the world wide Web accessed February 2004) National nanotechnology initiative: for students K-12. www.nanogowhtm html http:lluww This Activity may be reproduced for use in the subscriber's classroom. classroom 44B rnal of Chemical Education vol. 81 No. 4 April 2004 www JCE.DivCHED.orgExplanation / Answer
1. Citrate anions cover the entire surface of the nanoparticle and they serve as a barrier which prevents the nanoparticles from interacting. And as the surface gets negatively charged and since like charges repel each other, the nanoparticles do not attach to each other and hence, do not form aggregates.
2. Salt is an ionic compound and in solution, it dissociates into positive and negative ions. As a result, when salt solution is added to the nanoparticle solution, the ionic strength of the solution is increased and also, the charged barrier around each nanoparticle is disrupted. Thus, the naoparticles can interact and lead to aggregate formation.
On the other hand, sugar is a polar covalent compound. It dissolves in water but it does not dissociate in solution. Consequently, there is no effect on the ionic strength or the charged barrier around the nanoparticles and thus, no aggregation takes place.
3. Unfortunately, I do not see any Part B in your screenshot and so, I do not know which effect is it referring to.
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