Question

                                                            

造紙廠會(huì)產(chǎn)生含氫氧化鈉的廢水，需經(jīng)處理呈中性后排放．為測(cè)定此廢水中氫氧化鈉的質(zhì)量分?jǐn)?shù)，小明取40g廢水樣品加入到錐形瓶中，逐滴加入10%的稀硫酸，至恰好完全反應(yīng)時(shí)，消耗稀硫酸49g．計(jì)算廢水中氫氧化鈉的質(zhì)量分?jǐn)?shù)．                        

Answer 1

【考點(diǎn)】根據(jù)化學(xué)反應(yīng)方程式的計(jì)算；有關(guān)溶質(zhì)質(zhì)量分?jǐn)?shù)的簡(jiǎn)單計(jì)算．         

【專題】壓軸實(shí)驗(yàn)題；溶質(zhì)質(zhì)量分?jǐn)?shù)與化學(xué)方程式相結(jié)合的計(jì)算．         

【分析】利用恰好完全反應(yīng)所消耗硫酸的質(zhì)量，根據(jù)反應(yīng)的化學(xué)方程式，計(jì)算廢水中氫氧化鈉的質(zhì)量，利用質(zhì)量守恒定律計(jì)算所取廢水質(zhì)量；最后利用溶液中溶質(zhì)的質(zhì)量分?jǐn)?shù)公式計(jì)算出廢水中氫氧化鈉的質(zhì)量分?jǐn)?shù)．         

【解答】解：反應(yīng)消耗硫酸的質(zhì)量為：49 g×10%=4.9 g                  

設(shè)廢水樣品中氫氧化鈉的質(zhì)量為x．                                

2NaOH+H₂SO₄=Na₂SO₄+2H₂O                                          

80      98                                                  

x      4.9 g                                                

                                                  

x==4g                                            

廢水中氫氧化鈉的質(zhì)量分?jǐn)?shù)為×100%=10%                          

答：廢水中氫氧化鈉的質(zhì)量分?jǐn)?shù)為10%．                            

【點(diǎn)評(píng)】根據(jù)質(zhì)量守恒定律，反應(yīng)后溶液的質(zhì)量與所加入稀硫酸的質(zhì)量差即所取廢水溶液的質(zhì)量．