问题 问答题

在MgCl2和AlCl3的混和溶液中,逐滴加入NaOH溶液直至过量,经测定,加入NaOH的物质的量和所得沉淀的物质的量的关系如图所示,则:

(1)图中C点表示当加入______molNaOH时,Al3+的存在形式是______(写化学式)

(2)图中线段OA:AB=______.

答案

根据图象可知,在滴加NaOH溶液到加入氢氧化钠为Amol时,沉淀量最大为0.2mol,说明氯化铝、氯化镁恰好完全反应,此时溶液为氯化钠溶液.继续滴加氢氧化钠,但在加入(B-A)mol时,沉淀物质的量最小为0.1mol,是氢氧化镁沉淀,所以加入Amol氢氧化钠是沉淀中有氢氧化镁0.1mol、氢氧化铝0.1mol;此时溶液为氯化钠、偏铝酸钠溶液.

(1)根据氢氧根守恒可知,沉淀量最大时加入的氢氧化钠n(NaOH)=2n[Mg(OH)2]+3n[Al(OH)3]=2×0.1mol+3×0.1mol=0.5mol,C点氢氧化铝完全溶解,根据铝元素、钠元素守恒可知n(NaAlO2)=n[Al(OH)3]=0.1mol,所以溶解氢氧化铝加入的氢氧化钠为0.1mol.所以加入的氢氧化钠的物质的量为0.5mol+0.1mol=0.6mol;C点氢氧化铝完全溶解,铝元素在溶液中以AlO2-存在.

故答案为:0.6;AlO2-

(2)OA表示滴加NaOH溶液是镁离子、铝离子完全沉淀是需要的氢氧化钠的物质的量,沉淀量最大时加入的氢氧化钠n(NaOH)=2n[Mg(OH)2]+3n[Al(OH)3]=2×0.1mol+3×0.1mol=0.5mol;AB表示溶解0.1mol氢氧化铝消耗的氢氧化钠的物质的量n(NaOH)=n[Al(OH)3]=0.1mol,所以线段OA:AB=0.5mol:0.1mol=5:1.

故答案为:5:1.

判断题
单项选择题

The day was star-crossed: Friday the 13th in the month of October, on the eve of the second looming anniversary of a devastating market crash. "I’m telling you, psychology is really funny. People get crazy in situations like that," said portfolio strategist Elaine Garzarelli. Last week Friday the 13th lived up to its frightful reputation. After drifting lower at a sleepy pace for most of the day, the Dow Jones industrial average abruptly lurched into a hair-raising sky dive in the final hour of trading.

The Bush Administration moved swiftly to avert any sense of crisis after the market closed. Declared Treasury Secretary Nicholas Brady: "It’s important to recognize that today’s stock market decline doesn’t signal any fundamental change in the condition of the economy. The economy remains well balanced, and the outlook is for continued moderate growth." But Massachusetts Democrat Edward Markey, who chairs a House subcommittee on telecommunications and finance, vowed to hold hearings this week on the stock market slide. Said he: "This is the second heart attack. My hope is that before we have the inevitable third heart attack, we pay attention to these problems."

Experts found no shortage of culprits to blame for the latest shipwreck. A series of downbeat realizations converged on Friday, ranging from signs of a new burst of inflation to sagging corporate profits to troubles in the junk-bond market that has fueled major takeovers. The singular event that shook investors was the faltering of a $6.75 billion labor management buyout of UAL, the parent company of United Airlines, the second largest U. S. carrier.

On one point most thoughtful Wall Streeters agreed: the market had reached such dizzying heights that a correction of some sort seemed almost inevitable. Propelled by favorable economic news and a wave of multibillion-dollar takeovers, stocks had soared more than 1,000 points since the 1987 crash. But by last August some Wall streeters were clearly worried.

The heaviest blow to the market came Friday afternoon. In a three-paragraph statement, UAL said a labor-management group headed by Chairman Stephen Wolf had failed to get enough financing to acquire United. Several banks had apparently balked at the deal, which was to be partly financed through junk bonds. The take-over group said it would submit a revised bid "in the near term,’ but the announcement stunned investors who had come to view the United deal as the latest sure thing in the 1980s buyout binge. Said John Downey, a trader at the Chicago Board Options Exchange: "The airline stocks have looked like attractive takeover targets. But with the United deal in trouble, everyone started to wonder what other deals might not go through.

What does the writer say of the stock market decline()

A. Such an acute Crisis usually precedes a boom

B. It will constitute attractive takeover targets

C. Investors have trouble plucking up courage

D.It triggered responses from various sectors