I can well remember that I was once asked to deliver a speech titled: “A Real Test in My Life” before the whole class at the age of 9!You can imagine how ____ (terrible) shy I was the moment I thought of that with so many eyes ____ (fix) upon me. I had no ____(choose) but to prepare for it, though. First of all, I was to draft the speech, which was just a piece of cake for me, a good writer. But the hard part____(lie) in my oral presentation from my memory---for to read from the paper was not allowed. The real moment began ____ I stood on the platform with my legs trembling and my mind blank. But my____(listen)were still waiting patiently without any signs of rushing me. Gradually I found myself back, giving out my speech with difficulty. After what seemed to be a hundred years, I found my audience applauding ----I made____! From then on ,my fear of talking before an audience ____(appear). Actually with my confidence building up, I now turn out to be a great speaker. Looking back, I know the greatest difficulty on our way ____ success is our fear. Overcome it ,____ we will be able to achieve our goals.

【提出问题】该牙膏中CaCO₃的质量分数是多少？

【查阅资料】1、氢氧化钡、氢氧化钠有和氢氧化钙相似的化学性质，能吸收二氧化碳生成碳酸钡沉淀和碳酸钠。2、碱石灰是氧化钙和氢氧化钠的固体混合物，能较好的吸收二氧化碳和水。3、浓硫酸具有较强的吸水性，可作为气体的干燥剂。盐酸是氯化氢气体溶于水得到的溶液，具有挥发性。碳酸氢钠可以和盐酸反应生成二氧化碳气体。
【实验装置】